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Sunday, February 3, 2019
Saturday, February 2, 2019
1. What is normalization? Explain different levels of normalization?
Check out the article Q100139 from Microsoft knowledge base and of
course, there's much more information available in the net. It'll be a
good idea to get a hold of any RDBMS fundamentals text book,
especially the one by C. J. Date. Most of the times, it will be okay
if you can explain till third normal form.
normalization. It's the controlled introduction of redundancy in to
the database design. It helps improve the query performance as the
number of joins could be reduced.
relationships while designing tables?
rarely as two tables with primary and foreign key relationships.
One-to-Many relationships are implemented by splitting the data into
two tables with primary key and foreign key relationships.
Many-to-Many relationships are implemented using a junction table with
the keys from both the tables forming the composite primary key of the
junction table.
It will be a good idea to read up a database designing fundamentals
text book.
they are defined. But by default primary key creates a clustered index
on the column, where are unique creates a nonclustered index by
default. Another major difference is that, primary key doesn't allow
NULLs, but unique key allows one NULL only.
providing a descriptive name, and format to the database. Take for
example, in your database, there is a column called Flight_Num which
appears in many tables. In all these tables it should be varchar(8).
In this case you could create a user defined datatype called
Flight_num_type of varchar(8) and use it across all your tables.
See sp_addtype, sp_droptype in books online.
inside a bit column?
false). Untill SQL Server 6.5 bit datatype could hold either a 1 or 0
and there was no support for NULL. But from SQL Server 7.0 onwards,
bit datatype can represent a third state, which is NULL.
Generally a candidate key becomes the primary key of the table. If the
table has more than one candidate key, one of them will become the
primary key, and the rest are called alternate keys.
A key formed by combining at least two or more columns is called
composite key.
supplied to that column while inserting data. IDENTITY columns and
timestamp columns can't have defaults bound to them. See CREATE
DEFUALT in books online.
Back to top
SQL Server architecture (top)
8. What is a transaction and what are ACID properties?
A transaction is a logical unit of work in which, all the steps must
be performed or none. ACID stands for Atomicity, Consistency,
Isolation, Durability. These are the properties of a transaction. For
more information and explanation of these properties, see SQL Server
books online or any RDBMS fundamentals text book.
Explain different isolation levels
An isolation level determines the degree of isolation of data between
concurrent transactions. The default SQL Server isolation level is
Read Committed. Here are the other isolation levels (in the ascending
order of isolation): Read Uncommitted, Read Committed, Repeatable
Read, Serializable. See SQL Server books online for an explanation of
the isolation levels. Be sure to read about SET TRANSACTION ISOLATION
LEVEL, which lets you customize the isolation level at the connection
level.
CREATE INDEX myIndex ON myTable(myColumn)
9. What type of Index will get created after executing the above statement?
Non-clustered index. Important thing to note: By default a clustered
index gets created on the primary key, unless specified otherwise.
What's the maximum size of a row?
8060 bytes. Don't be surprised with questions like 'what is the
maximum number of columns per table'. Check out SQL Server books
online for the page titled: "Maximum Capacity Specifications".
10. Explain Active/Active and Active/Passive cluster configurations
Hopefully you have experience setting up cluster servers. But if you
don't, at least be familiar with the way clustering works and the two
clusterning configurations Active/Active and Active/Passive. SQL
Server books online has enough information on this topic and there is
a good white paper available on Microsoft site.
11. Explain the architecture of SQL Server
This is a very important question and you better be able to answer it
if consider yourself a DBA. SQL Server books online is the best place
to read about SQL Server architecture. Read up the chapter dedicated
to SQL Server Architecture.
12. What is lock escalation?
Lock escalation is the process of converting a lot of low level locks
(like row locks, page locks) into higher level locks (like table
locks). Every lock is a memory structure too many locks would mean,
more memory being occupied by locks. To prevent this from happening,
SQL Server escalates the many fine-grain locks to fewer coarse-grain
locks. Lock escalation threshold was definable in SQL Server 6.5, but
from SQL Server 7.0 onwards it's dynamically managed by SQL Server.
13. What's the difference between DELETE TABLE and TRUNCATE TABLE commands?
DELETE TABLE is a logged operation, so the deletion of each row gets
logged in the transaction log, which makes it slow. TRUNCATE TABLE
also deletes all the rows in a table, but it won't log the deletion of
each row, instead it logs the deallocation of the data pages of the
table, which makes it faster. Of course, TRUNCATE TABLE can be rolled
back.
14. Explain the storage models of OLAP
Check out MOLAP, ROLAP and HOLAP in SQL Server books online for more
infomation.
15. What are the new features introduced in SQL Server 2000 (or the latest
release of SQL Server at the time of your interview)? What changed
between the previous version of SQL Server and the current version?
This question is generally asked to see how current is your knowledge.
Generally there is a section in the beginning of the books online
titled "What's New", which has all such information. Of course,
reading just that is not enough, you should have tried those things to
better answer the questions. Also check out the section titled
"Backward Compatibility" in books online which talks about the changes
that have taken place in the new version.
16. What are constraints? Explain different types of constraints.
Constraints enable the RDBMS enforce the integrity of the database
automatically, without needing you to create triggers, rule or defaults.
Types of constraints: NOT NULL, CHECK, UNIQUE, PRIMARY KEY, FOREIGN KEY
For an explanation of these constraints see books online for the pages
titled: "Constraints" and "CREATE TABLE", "ALTER TABLE"
17. Whar is an index? What are the types of indexes? How many clustered
indexes can be created on a table? I create a separate index on each
column of a table. what are the advantages and disadvantages of this
approach?
Indexes in SQL Server are similar to the indexes in books. They help
SQL Server retrieve the data quicker.
Indexes are of two types. Clustered indexes and non-clustered indexes.
When you craete a clustered index on a table, all the rows in the
table are stored in the order of the clustered index key. So, there
can be only one clustered index per table. Non-clustered indexes have
their own storage separate from the table data storage. Non-clustered
indexes are stored as B-tree structures (so do clustered indexes),
with the leaf level nodes having the index key and it's row locater.
The row located could be the RID or the Clustered index key, depending
up on the absence or presence of clustered index on the table.
If you create an index on each column of a table, it improves the
query performance, as the query optimizer can choose from all the
existing indexes to come up with an efficient execution plan. At the
same t ime, data modification operations (such as INSERT, UPDATE,
DELETE) will become slow, as every time data changes in the table, all
the indexes need to be updated. Another disadvantage is that, indexes
need disk space, the more indexes you have, more disk space is used.
Back to top
Database administration (top)
18. What is RAID and what are different types of RAID configurations?
RAID stands for Redundant Array of Inexpensive Disks, used to provide
fault tolerance to database servers. There are six RAID levels 0
through 5 offering different levels of performance, fault tolerance.
MSDN has some information about RAID levels and for detailed
information, check out the RAID advisory board's homepage
19. What are the steps you will take to improve performance of a poor
performing query?
This is a very open ended question and there could be a lot of reasons
behind the poor performance of a query. But some general issues that
you could talk about would be: No indexes, table scans, missing or out
of date statistics, blocking, excess recompilations of stored
procedures, procedures and triggers without SET NOCOUNT ON
written query with unnecessarily complicated joins, too much
normalization, excess usage of cursors and temporary tables.
Some of the tools/ways that help you troubleshooting performance
problems are: SET SHOWPLAN_ALL ON, SET SHOWPLAN_TEXT ON, SET
STATISTICS IO ON, SQL Server Profiler, Windows NT /2000 Performance
monitor, Graphical execution plan in Query Analyzer.
Download the white paper on performance tuning SQL Server from
Microsoft web site. Don't forget to check out sql-server-performance.com
20. What are the steps you will take, if you are tasked with securing an
SQL Server?
Again this is another open ended question. Here are some things you
could talk about: Preferring NT authentication, using server, databse
and application roles to control access to the data, securing the
physical database files using NTFS permissions, using an unguessable
SA password, restricting physical access to the SQL Server, renaming
the Administrator account on the SQL Server computer, disabling the
Guest account, enabling auditing, using multiprotocol encryption,
setting up SSL, setting up firewalls, isolating SQL Server from the
web server etc.
Read the white paper on SQL Server security from Microsoft website.
Also check out My SQL Server security best practices
21. What is a deadlock and what is a live lock? How will you go about
resolving deadlocks?
Deadlock is a situation when two processes, each having a lock on one
piece of data, attempt to acquire a lock on the other's piece. Each
process would wait indefinitely for the other to release the lock,
unless one of the user processes is terminated. SQL Server detects
deadlocks and terminates one user's process.
A livelock is one, where a request for an exclusive lock is
repeatedly denied because a series of overlapping shared locks keeps
interfering. SQL Server detects the situation after four denials and
refuses further shared locks. A livelock also occurs when read
transactions monopolize a table or page, forcing a write transaction
to wait indefinitely.
Check out SET DEADLOCK_PRIORITY and "Minimizing Deadlocks" in SQL
Server books online. Also check out the article Q169960 from Microsoft
knowledge base.
22. What is blocking and how would you troubleshoot it?
Blocking happens when one connection from an application holds a lock
and a second connection requires a conflicting lock type. This forces
the second connection to wait, blocked on the first.
Read up the following topics in SQL Server books online: Understanding
and avoiding blocking, Coding efficient transactions.
23. Explain CREATE DATABASE syntax
Many of us are used to craeting databases from the Enterprise Manager
or by just issuing the command: CREATE DATABAE MyDB. But what if you
have to create a database with two filegroups, one on drive C and the
other on drive D with log on drive E with an initial size of 600 MB
and with a growth factor of 15%? That's why being a DBA you should be
familiar with the CREATE DATABASE syntax. Check out SQL Server books
online for more information.
24. How to restart SQL Server in single user mode? How to start SQL Server
in minimal configuration mode?
SQL Server can be started from command line, using the SQLSERVR.EXE.
This EXE has some very important parameters with which a DBA should be
familiar with. -m is used for starting SQL Server in single user mode
and -f is used to start the SQL Server in minimal confuguration mode.
Check out SQL Server books online for more parameters and their
explanations.
25. As a part of your job, what are the DBCC commands that you commonly
use for database maintenance?
DBCC CHECKDB, DBCC CHECKTABLE, DBCC CHECKCATALOG, DBCC CHECKALLOC,
DBCC SHOWCONTIG, DBCC SHRINKDATABASE, DBCC SHRINKFILE etc. But there
are a whole load of DBCC commands which are very useful for DBAs.
Check out SQL Server books online for more information.
26. What are statistics, under what circumstances they go out of date, how
do you update them?
Statistics determine the selectivity of the indexes. If an indexed
column has unique values then the selectivity of that index is more,
as opposed to an index with non-unique values. Query optimizer uses
these indexes in determining whether to choose an index or not while
executing a query.
Some situations under which you should update statistics:
1) If there is significant change in the key values in the index
2) If a large amount of data in an indexed column has been added,
changed, or removed (that is, if the distribution of key values has
changed), or the table has been truncated using the TRUNCATE TABLE
statement and then repopulated
3) Database is upgraded from a previous version
Look up SQL Server books online for the following commands: UPDATE
STATISTICS, STATS_DATE, DBCC SHOW_STATISTICS, CREATE STATISTICS, DROP
STATISTICS, sp_autostats, sp_createstats, sp_updatestats
27. What are the different ways of moving data/databases between servers
and databases in SQL Server?
There are lots of options available, you have to choose your option
depending upon your requirements. Some of the options you have are:
BACKUP/RESTORE, dettaching and attaching databases, replication, DTS,
BCP, logshipping, INSERT...SELECT, SELECT...INTO, creating INSERT
scripts to generate data.
28. Explian different types of BACKUPs avaialabe in SQL Server? Given a
particular scenario, how would you go about choosing a backup plan?
Types of backups you can create in SQL Sever 7.0+ are Full database
backup, differential database backup, transaction log backup,
filegroup backup. Check out the BACKUP and RESTORE commands in SQL
Server books online. Be prepared to write the commands in your
interview. Books online also has information on detailed
backup/restore architecture and when one should go for a particular
kind of backup.
29. What is database replicaion? What are the different types of
replication you can set up in SQL Server?
Replication is the process of copying/moving data between databases on
the same or different servers. SQL Server supports the following types
of replication scenarios:
* Snapshot replication
* Transactional replication (with immediate updating subscribers,
with queued updating subscribers)
* Merge replication
See SQL Server books online for indepth coverage on replication. Be
prepared to explain how different replication agents function, what
are the main system tables used in replication etc.
30. How to determine the service pack currently installed on SQL Server?
The global variable @@Version stores the build number of the
sqlservr.exe, which is used to determine the service pack installed.
To know more about this process visit SQL Server service packs and
versions.
Back to top
Database programming (top)
31. What are cursors? Explain different types of cursors. What are the
disadvantages of cursors? How can you avoid cursors?
Cursors allow row-by-row prcessing of the resultsets.
Types of cursors: Static, Dynamic, Forward-only, Keyset-driven. See
books online for more information.
Disadvantages of cursors: Each time you fetch a row from the cursor,
it results in a network roundtrip, where as a normal SELECT query
makes only one rowundtrip, however large the resultset is. Cursors are
also costly because they require more resources and temporary storage
(results in more IO operations). Furthere, there are restrictions on
the SELECT statements that can be used with some types of cursors.
Most of the times, set based operations can be used instead of
cursors. Here is an example:
If you have to give a flat hike to your employees using the following
criteria:
Salary between 30000 and 40000 -- 5000 hike
Salary between 40000 and 55000 -- 7000 hike
Salary between 55000 and 65000 -- 9000 hike
In this situation many developers tend to use a cursor, determine each
employee's salary and update his salary according to the above
formula. But the same can be achieved by multiple update statements or
can be combined in a single UPDATE statement as shown below:
UPDATE tbl_emp SET salary =
CASE WHEN salary BETWEEN 30000 AND 40000 THEN salary + 5000
WHEN salary BETWEEN 40000 AND 55000 THEN salary + 7000
WHEN salary BETWEEN 55000 AND 65000 THEN salary + 10000
END
Another situation in which developers tend to use cursors: You need to
call a stored procedure when a column in a particular row meets
certain condition. You don't have to use cursors for this. This can be
achieved using WHILE loop, as long as there is a unique key to
identify each row. For examples of using WHILE loop for row by row
processing
Write down the general syntax for a SELECT statements covering all the
options.
Here's the basic syntax: (Also checkout SELECT in books online for
advanced syntax).
SELECT select_list
[INTO new_table_]
FROM table_source
[WHERE search_condition]
[GROUP BY group_by__expression]
[HAVING search_condition]
[ORDER BY order__expression [ASC | DESC] ]
32. What is a join and explain different types of joins.
Joins are used in queries to explain how different tables are related.
Joins also let you select data from a table depending upon data from
another table.
Types of joins: INNER JOINs, OUTER JOINs, CROSS JOINs.
OUTER JOINs are further classified as LEFT OUTER JOINS, RIGHT OUTER JOINS and FULL
OUTER JOINs are further classified as LEFT OUTER JOINS, RIGHT OUTER JOINS and FULL
OUTER JOINS.
33. Can you have a nested transaction?
Yes, very much. Check out BEGIN TRAN, COMMIT, ROLLBACK, SAVE TRAN and
@@TRANCOUNT
34. What is an extended stored procedure? Can you instantiate a COM object
by using T-SQL?
An extended stored procedure is a function within a DLL (written in a
programming language like C, C++ using Open Data Services (ODS) API)
that can be called from T-SQL, just the way we call normal stored
procedures using the EXEC statement. See books online to learn how to
create extended stored procedures and how to add them to SQL Server.
Yes, you can instantiate a COM (written in languages like VB, VC++)
object from T-SQL by using sp_OACreate stored procedure. Also see
books online for sp_OAMethod, sp_OAGetProperty, sp_OASetProperty,
sp_OADestroy. For an example of creating a COM object in VB and
calling it from T-SQL, see 'My code library' section of this site.
35. What is the system function to get the current user's user id?
USER_ID(). Also check out other system functions like USER_NAME(),
SYSTEM_USER, SESSION_USER, CURRENT_USER, USER, SUSER_SID(), HOST_NAME().
36. What are triggers? How many triggers you can have on a table? How to
invoke a trigger on demand?
Triggers are special kind of stored procedures that get executed
automatically when an INSERT, UPDATE or DELETE operation takes place
on a table.
In SQL Server 6.5 you could define only 3 triggers per table, one for
INSERT, one for UPDATE and one for DELETE. From SQL Server 7.0
onwards, this restriction is gone, and you could create multiple
triggers per each action. But in 7.0 there's no way to control the
order in which the triggers fire. In SQL Server 2000 you could specify
which trigger fires first or fires last using sp_settriggerorder
Triggers can't be invoked on demand. They get triggered only when an
associated action (INSERT, UPDATE, DELETE) happens on the table on
which they are defined.
Triggers are generally used to implement business rules, auditing.
Triggers can also be used to extend the referential integrity checks,
but wherever possible, use constraints for this purpose, instead of
triggers, as constraints are much faster.
Till SQL Server 7.0, triggers fire only after the data modification
operation happens. So in a way, they are called post triggers. But in
SQL Server 2000 you could create pre triggers also. Search SQL Server
2000 books online for INSTEAD OF triggers.
Also check out books online for 'inserted table', 'deleted table' and
COLUMNS_UPDATED()
37. There is a trigger defined for INSERT operations on a table, in an
OLTP system. The trigger is written to instantiate a COM object and
pass the newly insterted rows to it for some custom processing. What
do you think of this implementation? Can this be implemented better?
Instantiating COM objects is a time consuming process and since you
are doing it from within a trigger, it slows down the data insertion
process. Same is the case with sending emails from triggers. This
scenario can be better implemented by logging all the necessary data
into a separate table, and have a job which periodically checks this
table and does the needful.
38. What is a self join? Explain it with an example.
Self join is just like any other join, except that two instances of
the same table will be joined in the query. Here is an example:
Employees table which contains rows for normal employees as well as
managers. So, to find out the managers of all the employees, you need
a self join.
CREATE TABLE emp
(
empid int,
mgrid int,
empname char(10)
)
INSERT emp SELECT 1,2,'Vyas'
INSERT emp SELECT 2,3,'Mohan'
INSERT emp SELECT 3,NULL,'Shobha'
INSERT emp SELECT 4,2,'Shridhar'
INSERT emp SELECT 5,2,'Sourabh'
SELECT t1.empname [Employee], t2.empname [Manager]
FROM emp t1, emp t2
WHERE t1.mgrid = t2.empid
Here's an advanced query using a LEFT OUTER JOIN that even returns the
employees without managers (super bosses)
SELECT t1.empname [Employee], COALESCE(t2.empname, 'No manager') [Manager]
FROM emp t1
LEFT OUTER JOIN
emp t2
ON
t1.mgrid = t2.empid
39. What is the difference between Function and Stored Procedure.
40. What is the difference between Trigger and Stored Procedure.
39. What is the difference between Function and Stored Procedure.
Stored Procedure (SP)
|
Function (UDF - User Defined Function)
|
SP can return zero, single or multiple
values.
|
Function must return a single value (which
may be a scalar or a table).
|
We can use transaction in SP.
|
We can't use transaction in UDF.
|
SP can have input/output parameter.
|
Only input parameter.
|
We can call function from SP.
|
We can't call SP from function.
|
We can't use SP in SELECT/ WHERE/ HAVING
statement.
|
We can use UDF in SELECT/ WHERE/ HAVING
statement.
|
We can use exception handling using
Try-Catch block in SP.
|
We can't use Try-Catch block in UDF.
|
40. What is the difference between Trigger and Stored Procedure.
1. We can execute a stored procedure whenever
we want with the help of the exec command, but a trigger can only be executed
whenever an event (insert, delete, and update) is fired on the table on which
the trigger is defined.
|
|
2. We can call a stored procedure from inside
another stored procedure but we can't directly call another trigger within a
trigger. We can only achieve nesting of triggers in which the action (insert,
delete, and update) defined within a trigger can initiate execution of
another trigger defined on the same table or a different table.
|
|
3. Stored procedures can be scheduled through a
job to execute on a predefined time, but we can't schedule a trigger.
|
|
4. Stored procedure can take input parameters,
but we can't pass parameters as input to a trigger.
|
|
5. Stored procedures can return values but a
trigger cannot return a value.
|
|
6. We can use Print commands inside a stored
procedure for debugging purposes but we can't use print commands inside a
trigger.
|
|
7. We can use transaction statements like begin
transaction, commit transaction, and rollback inside a stored procedure but
we can't use transaction statements inside a trigger.
|
|
8. We can call a stored procedure from the
front end (.asp files, .aspx files, .ascx files, etc.) but we can't call a
trigger from these files.
|
|
9. Stored procedures are used for performing
tasks. Stored procedures are normally used for performing user specified
tasks. They can have parameters and return multiple results set.
|
|
10. The Triggers for auditing work: Triggers
normally are used for auditing work. They can be used to trace the activities
of table events.
|
PowerBuilder frequently asked questions by top companies
PowerBuilder frequently asked questions by top companies
Question 1
What
is the difference between SetTrans() and SetTransObject()?
Answer
In
simple terms, SetTrans() gives you no control on the transactions. It
automatically connects to and disconnects from the database after each
Retrieve() and Update() function. It is useful when the number of connections
are limited, but, you can't use this for multi-table update. On the other hand
SetTransObject() gives you full control over the transactions. It is your responsibility
to connect to and disconnect from the database and also, you need to issue
COMMIT/ROLLBACK statements. This method is more efficient since there is no
connect/disconnect overhead for each database operation.
Question 2
List
all the buffers that a DataWindow control maintains.
Answer
Primary!,
Delete!, Filter!, Original!, and one buffer for the edit control.
Question 3
When
the DataWindow is set to ReadOnly, What buffers PowerBuilder maintains for the
DataWindow Control?
Answer
PowerBuilder
maintains all the four buffers, i.e., Primary!, Delete!, Filter!, Original!.
Question 4
How
do you change the SQL Statement of a DataWindow at run-time?
Answer
You
can either use the Modify() or .Object notation to change the SQL statement of
a DataWindow control. In the SQLPreview event, you can change it using
SetSQLPreview(). Outside SQLPreview event, you can call SetSQLSelect().
Question 5
The
new .Object notation syntax for the DataWindow control replaces the Modify()
function. Explain.
Answer
No,
it doesn't completely replace Modify() function. You can create objects such as
rectangle, text objects in the DataWindow object using the CREATE statement in
the Modify() function. This can't be done with the .Object notation.
It is also not possible to refer to the data by column name dynamically, which
can be done using Modify().
Question 6
Describe
where you can't use .Object notation for a DataWindow control instead of the
Modify()?
Answer
You
can't create objects in the DataWindow object dynamically using the .Object
notation.
Question 7
How
do you change the DataWindow object of a DataWindow control at run-time?
Answer
DataWindow_Control_Name.DataObject
= 'New_DataWindow_Object_Name'
Question 8
What
will happen if you pass extra retrieve arguments to the Retrieve() function for
the DataWindow control?
Answer
PowerBuilder
ignores extra arguments.
Question 9
What
will happen if you pass no arguments to the DataWindow's Retrieve() function,
when the DataWindow is expecting some arguments?
Answer
PowerBuilder
prompts you for the arguments at run-time.
Question 10
Can
you use an array as an argument to the DataWindow's Retrieve() function? If
yes, How and where it is useful?
Answer
Yes,
you can use PowerBuilder array as an argument to the Retrieve() function. This
is useful when you use IN clause in the SELECT statement of the DataWindow's
source.
Question 11
What would be the row status in the destination DataWindow when a row is copied from another DataWindow using RowsCopy() function?
Answer
NewModified!
Question 12
What would be the row status in the destination DataWindow when a row is copied from another DataWindow using RowsMove() function?
Answer
NewModified!
Question 13
I
would like to allow the user to print selected rows. How it can be done?
Answer
Have
a hidden DataWindow control or a DataStore and assign the same DataWindow object
that you are using to display on the window. Copy selected rows to the
DataStore or the hidden DataWindow control (You can use RowsCopy() function)
and print the DataStore or the hidden DataWindow control.
Question 14
What
are the different statuses a row in a DataWindow can have?
Answer
New!,
NewModified!, DataModified!, NotModified!
Question 15
What
are the different statuses a column in a DataWindow row can have?
Answer
DataModified!,
NotModified!
Question 16
Explain
the use of AcceptText() function.
Answer
This
function applies the content of the edit control to the primary buffer after
validating the data. PowerBuilder applies the edit control content to the
Primary buffer whenever user press tab or click on another column within the
DataWindow. if the user change the value of a single column and doesn't press
either tab or click on another column, PowerBuilder will not copy the changed
data, that means the changes will not be applied in the database. Calling the
AcceptText() function solves this problem. You can also specify to the Update()
via argument to call AcceptText() internally before applying the changes to the
database.
Question 17
When
you update the DataWindow, what would be the each row status in the DataWindow
when the update is successful?
Answer
NotModified!
Question 18
You
have deleted few rows, say 10 rows from a DataWindow, and update the
DataWindow. How many rows would be available in the Deleted buffer after
successful update?
Answer
Zero
Rows.
Question 19
Explain
the advantages and disadvantages of calling AcceptText() function from the
ItemChanged event of a DataWindow control.
Answer
AcceptText()
function shouldn't be called from ItemChanged event. This is because,
AcceptText() function triggers the ItemChanged event. That means, calling
AcceptText() in the ItemChanged event will go into a loop. So, there are only
disadvantages, no advantages. If you really need to call AcceptText() from
ItemChanged event, create a user-defined event and post that event from the ItemChanged
event.
Question 20
How
do you change the default DataWindow error message title?
Answer
Assign
the application object's 'DataWindowMessageTitle' attribute with the new
DataWindow error box title.
Question 21
Assume,
you have marked a field as 'Required'. At run-time user tabs into that field
and tabs out without entering a value in that field. Will PowerBuilder force
the user for specifying a value? If not, how do you force the user for
specifying the value?
Answer
As
long as the user do not change (In this context, do not enter the data) the
column's value, PowerBuilder do not force entering a value. The solution to
this problem is, Call FindRequired() function before you update the DataWindow.
Question 22
Explain
the DataWindow validation.
Answer
PowerBuilder
checks whether the data is changed or not by comparing the edit control value
with primary buffer. It checks for the data type correctness, if the data is
changed. Wrong data type will trigger ItemError event. When the data passes the
data type checking, it executes the validation rule. Invalid data will trigger
ItemError event. Correct data will trigger ItemChanged event. If the
ItemChanged event returns zero, it will trigger ItemFocusChanged event, otherwise
ItemError will be triggered. Depending on the ItemError event's return value,
either the cursor remains in the same column or will go to the next higher tab
sequence's field (In this case, ItemFocusChanged event will be triggered).
Question 23
When
two DataWindow are being shared, what exactly would be shared and are there any
restrictions?
Answer
The
presentation is not shared. The data (buffers including Delete! and Filter!)
and the sort criteria is shared. There are few restrictions, which include,
Crosstab DataWindow windows can't share data, the client and the server in the
distributed computing mechanism can't share data. you can turn on the query
mode only for the primary DataWindow. If a DataWindow is sharing data with a
nested DataWindow, the handle to the nested DataWindow becomes invalid with
each retrieval. So, GetChild() and ShareData() need to be called each time a
nested DataWindow is retrieved.
Question 24
What
is difference between 'prompt for criteria' and 'Query Mode'?
Answer
'Prompt
For Criteria' as the name says, prompts for the criteria--for all those columns
that were marked--in its own display dialog box and ignores the DataWindow you
have painted. It also ignores the tab sequence number, i.e., prompts even if
the tab sequence is zero. 'QueryMode' is more flexible than the 'Prompt for
Criteria', and it uses the DataWindow you have painted. It allows querying on
all non-zero tab sequence columns in the DataWindow and you do not mark any
column for this purpose. The former one promts for the values every time
Retrieve() is called, where as the later one takes values only when you turn it
on--by enabling QUERYMODE property.
Question 25
Say,
you have a DataWindow which returns 10,000 rows. After retrieving few rows,
say, 100 rows, you have decided not to retrieve the rest of the rows. Explain
different methods of canceling the result set.
Answer
There
are two ways to accomplish this.
In the first method, you can call DBCancel() to cancel the query from a
CommandButton Clicked event or in other event. However, once PowerBuilder
starts retrieving the data, it will not give the control to the user till it
completes retrieval. So, you need to put some code/comments in RetrieveRow
event which will yield a little bit.
In the second method, you can just return 1 from the RetrieveRow event.
In the second method, you can just return 1 from the RetrieveRow event.
Question 26
Say,
you have a DataWindow with two fields, emp_name, emp_address. Now, the focus is
on the emp_name field. When the user press tab, what would be the return value
of GetColumnName() from A.) ItemChanged and B.) ItemFocusChanged events?
Answer
GetColumnName()
returns 'emp_name' in the ItemChanged event and 'emp_address' in the
ItemFocusChanged event.
Question 27
Explain
the steps that are required to update a multiple-table DataWindow?
Answer
In
short, using the Modify function or .Object notation, you need to make one
table updatable. You also need to set the primary keys for that table. Then
update the DataWindow with FALSE argument for the reset option in the Update()
function. After successful update, make the second table updatable and the
first one not-updatable. Now call Update() function with TRUE for the reset
option (If there are more than two tables, use the TRUE option to the last
table to be updated). Commit after successful update and Rollback on
unsuccessful update.
Question 28
What
you have to do if you want the PowerBuilder to prompt for the sort criteria at
run-time?
Answer
Set
the sort criteria to NULL value using the SetSort() function and call Sort()
function.
Question 29
How
many times PowerBuilder will retrieve data from the child DataWindow in the
following situation. A DataWindow has a field with DDDW edit style. There are
1000 rows in the parent DataWindow.
Answer
It
retrieves only once. The thumb rule here is that, PowerBuilder retrieves data
from the child DataWindow only when the child DataWindow do not have data in
it.
Question 30
What
command/function you use to select a row?
Answer
SelectRow()
function.
Question 31
If
there are 10 rows selected in a DataWindow, and if you call DeleteRow()
function, how many rows will be deleted? Explain.
Answer
DeleteRow()
has nothing to do with the row selection. It deletes only one row that you
specify as the argument to it. If you want to delete all the selected rows, you
need to call DeleteRow() in a loop for each selected row (You can find the
selected row by calling GetSelectedRow() function).
Question 32
You
have defined a composite DataWindow 'd_master' which has two DataWindows
'd_emp_info', 'd_emp_paychecks'. 'd_emp_info' takes one argument and
'd_emp_paychecks' takes two arguments. 'd_master' is placed in 'DataWindow_1'
DataWindow control. DataWindow_1.Retrieve( Arg1, Arg2, Arg3 ) will retrieve
data without prompting. Do you agree? Explain.
Answer
PowerBuilder
prompts for the retrieval arguments. This is because, you can't specify
retrieval arguments in the Retrieve() function for the nested DataWindows.
Instead, you need to set Nested_Arguments attribute using the Modify() function
or .Object notation.
Question 33
What
will happen when you pass a wrong argument to the Modify() function?
Answer
Returns
the error code, but doesn't trigger any event such as DataWindow dbError or
Error. However, doing the same using .OBJECT notation will generate error and
trigger DataWindow Error event.
Question 34
What
will happen when you use a wrong expression for a DataWindow in the .Object
notation?
Answer
Will
trigger Error event of the DataWindow control.
Question 35
What
is the difference between 'Error' and 'dbError' events in a DataWindow control?
Answer
DbError
event is fired when a database related error occurs. Error event at the
DataWindow control level is triggered when a wrong expression is encountered in
the .Object notation, or a OLE/OCX related error occurs. For database errors,
if you do not write any code in DBError event, PowerBuilder displays the error
in its own dialog box. In the later case, if you do not code to DataWindow
ERROR event, it will fire Application SystemError event. If there is no code in
that event, PowerBuilder displays the error message and terminates the
application.
Question 36
Explain
the following error: 'Row(s) changed between retrieve and update'. Also explain
how you will get rid of that error?
Answer
PowerBuilder
reports this error when some one/process updates the row after you retrieve it
but before apply the changes. POWERBUILDER detects this type of error when you
include the TimeStamp column in the DataWindow or use the 'Key columns and
Updatable columns' in the WHERE criteria. We can't avoid this error. The
solution to this problem would be, reselect the row that caused the error and
display it to the user with appropriate message and then update the database
again. You can use ReSelectRow() function to get the latest values for the
error row.
Question 37
What
is concurrency control? How do you control it from the PowerBuilder?
Answer
When
multiple users are working on the same data, we have to make sure that we don't
corrupt others changes, either by updating their changes without looking at
them or by any other means. When we apply changes to the database, we have to
make sure that no body changed the data between your read and update. This can
be controlled (not exactly controlling, but, we can detect) using the
appropriate WHERE clause option in the update properties in the DataWindow
painter.
Question 38
Explain
different ways of generating a serial number for a column in a table. Explain
ways in PowerBuilder and in the database. Which method you recommend?
Answer
This
has to be controlled from the database, not from the PowerBuilder. This is
because, a unique serial number generated by a POWERBUILDER client may not be
unique for other user or when it is put in the database. If the database
supports auto incrementing (Different database vendors implement it in
different ways, for ex: sybase implements using Identity column property,
Watcom calls AutoIncrement, Oracle selects from a special table), then there is
no problem. Otherwise, you can use a single row single column table to generate
serial no. The method you choose might depend on the performance issues and
number of expected inserts and other factors.
Question 39
I
want to execute a stored procedure that is defined in the database, using the
function call notation. What I need to do?
Answer
Define
a function that refers to the stored procedure, in the transaction object and
start using the function. It is something like declaring an external function,
however, you can't declare a function for a stored procedure at any object
other than a transaction object.
Question 40
Explain
the steps involved in inserting your a layer between 'transaction' object and
'SQLCA'.
Answer
Create
a standard class user object by inheriting from 'Transaction' object. Define
the attributes and functions that you need. Now, ask the SQLCA to be of type
YourTransactionObject instead of TRANSACTION object. This you can do in the
application painter.
Question 41
Write
the code to protect existing data from changes by the user in a DataWindow and
allow adding new rows.
Answer
DataWindow_1.Object.Column1.Protect
= '1~tIf(IsRowNew(),0,1)'
Question 42
Explain
the method you follow when you want to skip printing all pages that are
divisible by 7 (seven)?
Answer
Well,
you can write code for the PrintPage event of a DataWindow control. Check
whether the page number is divisible by seven, if so, then return 1.
Question 43
I
want to use the value passed in the retrieval arguments in the DataWindow. What
I need to do?
Answer
If
you are using PowerBuilder version 4.0 or above, you should be able to see the
retrieval arguments under in the 'Columns' listbox in the 'Expression' dialog
box. So, you can use it as if it is a column.
Question 44
The
following situation triggers 'SystemError' event at the application object.
Explain. You are trying to update a table on which you don't have update
privilege.
Answer
This
will not trigger the SystemError event, since it is a database & DataWindow
related error. It triggers DataWindow DbError event. If there is no script for
that event, PowerBuilder displays the error message in the default way.
Question 45
You
got 'Row(s) changed between retrieve and update' error. Now, you want to select
the latest value of that changed row. How you do that?
Answer
Use
ReSelectRow() function.
Question 46
In
a DataWindow, there are few fields with validation rules, and few fields with
script in the ItemChanged event. I want to display custom error message when
data doesn't go through the ItemChanged event, but want to display default
error messages when the data doesn't go through the validation rules. What
should I do?
Answer
Well,
define an instance variable. Turn it one when you decide the data is invalid in
the ItemChanged event. In the ItemError event, return appropriate return code
depending on the instance variable value and reset the instance variable to
it's default value appropriately.
Question 47
I
want to find out all the fields that doesn't have values and have 'Required'
attribute turned on. What should I do?
Answer
Call
FindRequired() function before you call Update() function.
Question 48
Can
I store some data in the DataWindow? If yes, How?
Answer
Select
Rows/Data from the menu when you are in the DataWindow painter design mode and
add data to the DataWindow and save the DataWindow. The data now is stored as
part of the DataWindow definition.
Question 49
What
I need to do if I want the child DataWindow shouldn't retrieve the data
automatically?
Answer
Store
an empty row in the child DataWindow. PowerBuilder do not retrieve data from
the child DataWindow since it sees data inside it. You can store data in the
child DataWindow, by selecting Rows/Data from the menu when you are in the
DataWindow painter design mode.
Question 50
How
many DataWindow can share the data from a DataWindow?
Answer
There
is no limitation on how many DataWindows can share data from the first primary
DataWindow or from the secondary DataWindow that work as primary DataWindow for
other DataWindows.
Question 51
What
is the difference between a DataWindow and a DataStore object?
Answer
DataStore
is nothing but a DataWindow without interaction related events and functions.
DataStore has less overhead compared to DataWindow since the DataStore object
do not have interaction related overhead. You can use DataStore as a parameter
to a remote object function/event in the distributed computing and OLE
automation, where as DataWindow can not be used in those situations.
Question 52
Can
a DataWindow share the data from a DataStore?
Answer Yes.
Question 53
I
have a table in which one column is of 'LongBinary' data type. Can I update
this column using DataWindow? If yes, How?
Answer
A
regular DataWindow do not support BLOB data types such as 'Long Binary',
Sybase's Image & Text data type columns. You need to use 'DATABASE BLOB'
object in the DataWindow object. You can update the database normally when you
follow these steps.
Question 54
What
is the difference between a 'Computed Column' and 'Computed Field'?
Answer
'Computed
Column' is a column that you define as part of the SELECT statement. These
values are calculated by the database and sent to the PowerBuilder client.
'Computed Field's' we define in the DataWindow bands and PowerBuilder
calculates these values, not the database. Depending on your computing model
'Fat Client' or 'Thin Client' you can decide which one to use. If it is 'Fat
Client' model, use 'Computed Fields', otherwise use 'Computed Columns'.
Question 55
Can
you change the value of a 'Computed Field' at run-time?
Answer
No,
you can't the Computed field value directly. However, you can change the column
value that are part of the Computed field expression, by that Computed field
value will be changed automatically.
What
is a Dynamic DataWindow and how do you create a Dynamic DataWindow?
Answer
Dynamic
DataWindow is the DataWindow that is not painted at design-time, instead it is
created at run-time. This is useful when you don't know the exact columns that
you need to include in the DataWindow at design time. You need to use
SyntaxFromSQL() function and Create() function to create a DataWindow
dynamically.
Question 57
How
can I search a DataWindow?
Answer
Use
Find() function.
Question 58
In
a DataWindow validation rule, how can I refer to the data that is entered by
the user?
Answer
Call
GetText() function in the validation rule to get the data entered by the user.
If you want to paint the same in the Database painter, you can use @name where
name can be any text. PowerBuilder automatically converts @name to GetText() in
the DataWindow validation rule when you paint a DataWindow that uses that
column.
Question 59
Explain
how 'Retrieve Only Needed' works.
Answer
By
default, PowerBuilder displays the first row on the screen when it completes
retrieving all the result set. That means, if there is huge result set, user
has to wait for long time to see the first row on the screen. If you turn on
'RetrieveOnlyAsNeeded' property, PowerBuilder retrieves only those rows that
fit on one screen. That means, user will see the data quickly. When the user
scrolls, PowerBuilder retrieves again (as many rows as required). This option
might affect the database server performance also, since the result is queued at
the database till PowerBuilder client completes retrieving.
Question 60
What
should I do if I want to display rows as soon as they are retrieved from a
DataWindow?
Answer
Write
code in the RetrieveRow event, at least a single line comment. And also set the
'Async' attribute in the DbParm property of the transaction object.
Question 61
Say,
you have a DataWindow 'd_emp' which has a field 'emp' with DDLB edit style.
When you read the field value using GetItemxxxxxxxx() function, what value is
returned, 'Display Value' or 'Data Value'? What you need to do to get other
value?
Answer
Use
the LookupDisplay() function.
Question 62
How
do you handle variable length text fields in a DataWindow?
Answer
Set
the 'AutoSizeHeight' property in the detail band of the DataWindow when you are
in the DataWindow painter design mode.
How
to retrieve multiple result set of a stored procedure in a single DataWindow?
Answer
A
DataWindow can retrieve only one result set at a time. If you want to retrieve
other result sets also, you can change the result set number either by Modify()
function or using .Object notation. When you change the result set, make sure
the number of columns and data types match with the existing DataWindow
definition.
Question 64
How
to retrieve a particular result set of a stored procedure in a DataWindow?
Answer
You
need to suffix the result set number to the stored procedure name separated by
semicolon.
Question 65
How
to load a text file in a DataWindow?
Answer
Well,
you can use ImportFile() function.
Question 66
What
is a CrossTab presentation Style DataWindow? What are the places you can use
this type of DataWindow?
Answer
Crosstab
presentation style DataWindow allows to shorten the length of the report and
display the data in a two-dimensional spreadsheet like report. One dimension
displays in columns and the other as rows.
Question 67
How
do you update a 'Group' presentation style DataWindow?
Answer
A
DataWindow with 'Group' presentation style can't be updated.
Question 68
How
do you update a 'OLE' presentation style DataWindow?
Answer
OLE
presentation style DataWindow is only for display, you can't update that
DataWindow.
Question 69
What
are code tables and how you can use them in a DataWindow?
Answer
Code
tables are used for translation. Typical use of code table is to display long
description about the data, say, 'New York' and store the abbreviation in the
database, say, 'NY'. You can use code tables in the DataWindow for the EditMask
edit style only.
Question 70
What
is the difference between a 'column name' and 'database column name'. Can you
change any of these at painting time? If yes, How?
Answer
'Column
Name' is the name of the column in the DataWindow. You always refer to this
name when you want to change the column attributes. You can change the column
name in the DataWindow. The 'Database column name' is the name of the column in
the database and you can't change this name. Typically, this name is prefixed
with the database and table and owner name. You can see both column and
database column names by selecting 'Rows/Columns' in the DataWindow when you
are in the DataWindow design mode.
Question 71
You
have a DataWindow that has 100 rows. I want to append the rows to the existing
rows when I retrieve next time in that DataWindow. Explain the required steps
to do this.
Answer
Return
2 in the RetrieveStart event of that DataWindow control.
Question 72
What
is the event from which I can see the exact SQL statement that is being sent to
the database by PowerBuilder?
Answer
SQLPreview
event of the DataWindow control.
Question 73
How
to refer to a DataWindow column by the column number in the 'Describe()' and
'Modify()' functions.
Answer
You
need to prefix the column number with pound (#). For example,
DataWindow_1.Modify( '#10.TabSequence=0' ) sets the column number ten's tab
order to zero.
Question 74
How
to update a DataWindow that has 'Stored Procedure' as the data source?
Answer
Go
to the update properites of the DataWindow by selecting Rows/Update properties
from the menu when you are in the design mode in the DataWindow painter. Type
the table name to update in the 'Table' prompt. Make sure the column names and
data types are same.
Question 75
What
are the uses of a DataWindow with 'External' data source?
Answer
'External'
DataWindows are useful when you want to use the power of DataWindows, even
though you are not retrieving the data from the database. Some of the features
which would be more difficult to implement without using a DataWindow are,
sorting, filtering, printing, exporting data into different formats, print
previewing/zooming and so on.
Question 76
How
many 'OLE DATABASE' columns you can use in one DataWindow?
Answer
Well,
you can paint as many OLE Database BLOBs as you wish in a DataWindow. However,
the update is not going to take place when you place more than one OLE Database
BLOB object in a DataWindow.
Question 77
What
are different types of windows available in PowerBuilder?
Answer
There
are six different types of windows available in PowerBuilder. Those are Main,
Popup, Child, Response, MDI Frame, MDI Frame with Microhelp.
If
I create a response window and open that window in an MDI frame using
OpenSheet(), what will happen?
Answer
When
you open a window in a MDI frame using OpenSheet() or OpenSheetWithParm()
functions, that window get the sheet properties, irrespective of the window
type. That means, when you open the response window using one of those
functions, the window will behave like any other sheet, i.e., gets maximize,
minimize, close controls on the title bar.
Question 79
Explain
how a popup window is different from a child window?
Answer
Popup
window can go beyond the parent window borders and Popup window is always on
the top. On the other hand, the Child window can't go beyond parent window
borders. Child window is never considered as an Active window from the
programming perceptive.
Question 80
What
is MDI_1?
Answer
MDI_1
control represents the 'Client Area' in a 'MDI frame' or 'MDI frame with
Microhelp'. That means, all the window area other than 'Titlebar', 'Menu',
Microhelp statusbar' is MDI_1. When you paint any object in the MDI window, you
need to resize the client area programmatically by referencing MDI_1,
otherwise, MDI_1 control size is not determined. That means, we can't see any
sheet that we open in the client area, unless we resize the MDI_1 control.
Question 81
What
should I do if I want to paint a window control in a MDI Frame window?
Answer
You
need to resize the MDI_1 control. Window's resize event is the good candidate
to write the script for MDI_1 control re-sizing. You need to reduce the size of
the MDI_1 control by the size of all the controls that you have placed in the
window.
Question 82
Can
I have multiple MDI frame windows in the same application?
Answer
Well,
technically, you can have multiple MDI windows in the same application. You can
call Open() function twice, one for each MDI window. Please note that, the user
might think that, two applications are running, since two different windows
will appear with different menus.
Question 83
I
need to declare an Instance variable for a DataWindow control ONLY, in a
window. What should I do?
Answer
When
you declare an instance variable at a window, it is accessible to all controls
in the window. First of all, you can't declare an Instance/Shared variable for
a specific control in a window. If you have the need of that, you need to
create a user object of that specific control and declare instance/shared
variables in the user object. Then place the user object in the window. In
summary, a window control can't have it's own instance/shared variables, but
the user object can (in the user object painter ONLY, not in Window Painter).
Question 84
Can
I have a global and local variable with the same name?
Answer
Yes,
You can have global and local/instance variable with the same name.
Question 85
You
have declared a global variable xyz and a local variable xyz in the clicked
event of a CommandButton. When you refer to xyz in the CommandButton's clicked
event, which variable is referred? Global or Local?
Answer
Well,
when you refer to xyz variable, POWERBUILDER search for the variable in local,
instance/shared, instance/shared at the ancestor, global order. That means, in
this case, the local variable is referred. To refer to the global variable
which has the same name of a local variable, you need to prefix double colon
before the variable name.
Question 86
How
a 'Shared Variable' is different from a 'Instance Variable'?
Answer
Well,
the value of an instance variable in each instance is independent of other
instances. Instance variables are created when the object is created and will
be destroyed when the object is destroyed. On the other hand, the shared
variable is shared between different instances of the variable. That means,
changing the shared variable in one instance will affect other instances. The
shared variable is created when the FIRST instance of the object is created and
is destroyed when the application is closed. You can't refer to an object's
shared variable when none of the instance is open, even though the shared
variables exists in the memory.
Question 87
Tell
me some situations where you need to use shared variables.
Answer
One
typical situation would be, counting the number of instances of a sheet.
Another situation will be, you can use the shared variable to prevent the user
updating the same record from multiple instances of the same window with
different values.
Question 88
When
a function argument is declared 'By ReadOnly', what you can do on that variable
and what you can't do?
Answer
You
can refer to that argument, you can change the value of the argument. But, you
can't assign another object to that object. For example, say, a DataWindow is
passed as a 'By ReadOnly' argument. You can change the value of any column/row
of that DataWindow, but you can't say: arg_DataWindow = Another_DataWindow. In
this case, you are assigning another object to this object. That means, you are
asking to change the pointer to refer to the new object instead of the original
object, which is not allowed when the argument is passed by 'By ReadOnly'.
Question 89
What
is the difference between passing a function argument 'By Value' and 'By
Reference'?
Answer
When
an argument is passed 'By Value', the changed value of the argument in the
called function will not be available in the calling object. On the other hand,
when the argument is passed 'By Reference', the changed value of the argument
in the called object IS AVAILABLE in the calling object. In case of 'By Value',
POWERBUILDER sends a copy of the object, where as a pointer is send when passed
by 'By Reference'.
Question 90
Can
you declare CONSTANTS in PowerBuilder?
Answer
From
version 5.0 onwards, you can declare constants in POWERBUILDER. For example:
CONSTANT APPEND_TO_ROWS 2. When you want to append to the existing rows in the
DataWindow when you retrieve next time, write 'return APPEND_TO_ROWS' instead
of 'return 2'. Using constants you can make the code more readable and also
more efficient (in some places).
Question 91
Explain
the use of ANY data type.
Answer
ANY
data type was introduced in version 4.0. You can use this data type when you
really not sure about the return value of function. For example, OLE 2.0
control and in OLE automation. You really don't know what object/error code
will be returned by the OLE client. Sometimes, those are compatible with POWERBUILDER
data types. In those cases, you can use this variable to store the return value
and CAST it to another data type before you operate on the value.
Question 92
How
do you declare a function that returns nothing?
Answer
Type
'(None)' without quotations in the 'Return Value' prompt when you are in the
function painter.
Question 93
How
to execute the ancestor event's script from the descendant's event?
Answer
You
can use CALL SUPER::EVENT_NAME syntax.
Question 94
What
will happen when you TRIGGER a non-existing event?
Answer
If
you trigger a non-existing event using the old syntax, TriggerEvent(), nothing
happens. In the new syntax, you can't trigger a non-existing event unless you
use DYNAMIC keyword. When you trigger the event dynamically, NULL value will be
returned.
Question 95
What
will happen when you TRIGGER an event that doesn't have any script?
Answer
Nothing
will happen. You are not allowed to capture the return value of an event which
returns nothing. NULL value is returned when you trigger an event which has no
script.
Question 96
What
is the difference between TriggerEvent() and PostEvent()?
Answer
TriggerEvent()
executes the specified event's script right away. PostEvent() posts the
requests in the operating system's queue. This doesn't mean the posted event's
script will be executed after completing the current script execution. It might
execute right away also, it depends on how many requests are in the Operations
system's message queue.
Question 97
What
is the difference between TriggerEvent() and Send()?
Answer
TriggerEvent()
JUST executes the specified event's script, but, it do not really trigger the
event. For example, triggering the window's 'Close' event will execute the
script written for that event, but, will not close the window. If you use
Send() function, it does both, i.e., executes the script and closes the window
also.
How
PowerBuilder executes events? Bottom-to-Top or Top-to-Bottom?
Answer Top-to-Bottom
Question 99
In
the inheritence hirerachy, How PowerBuilder search for a function?
Top-to-Bottom or Bottom-to-Top?
Answer
Bottom-to-Top
Question 100
Explain
different levels of attribute/method protection available in PowerBuilder?
Answer
Public,
Protected, Private, PrivateRead, PrivateWrite, ProtectedRead, ProtectedWrite
Question 101
How
do you pass a value to a window at opening time?
Answer
Use
either OpenWithParm() or OpenSheetWithParm() function depending on whether you
are trying to open a window as a window or a sheet.
Question 102
Explain
what a 'Message' object is and How it is useful in the programming?
Answer
'Message'
object contains the messages that are sent by the operating system and sent by
the POWERBUILDER scripts. It always contains only one message, that is the
latest one. When you use OpenWithParm(), OpenSheetWithParm(),
OpenUserObjectWithParm(), those parameters are placed in the 'Message' object
and you can access those parameters in the opening object from the 'Message'
object. Changing the values of the 'Message' object affects the event
execution. For example, changing the 'ReturnValue' of the Message object in the
window's CloseQuery event to 1 will stop the window being closed.
Question 103
What
is the difference between 'Close' and 'CloseQuery' event?
Answer
POWERBUILDER
triggers 'CloseQuery' event before it triggers 'Close' event. If 'CloseQuery'
event's script is not executed successfully (in terms of return value), 'Close'
event will never trigger.
Question 104
Explain
typical scripting that you do in the 'CloseQuery' event?
Answer
Typical
scripting would be, checking for unsaved work and prompting the user for the
same and take action depending on the user's response.
Question 105
What
should I do if I want to use '-' (hyphen) in identifiers in PowerScript?
Answer
Add
'DashesInIdentifiers=1' without quotations to the [POWERBUILDER] section in the
POWERBUILDER.INI file.
Question 106
Explain
different debugging mechanisms in PowerBuilder.
Answer
First
mechanism would be obviously the debug painter. You can also use TRACE flag to
log all the ODBC calls, /PBDEBUG to log the POWERBUILDER script execution.
Question 107
What
should I do if I want to call a Windows SDK API?
Answer
You
need to declare the Windows SDK API as an external function either locally or
globally depending on your need. Then only you can refer to that function in
PowerScript. If you have the same function name in PowerScript also, you can
alias the external function in the declaration.
Question 108
List
three PowerBuilder pronouns that we use to reduce hard-coding.
Answer
THIS,
PARENT, PARENTWINDOW
Question 109
How
'Parent' is different from 'ParentWindow'?
Answer
'Parent'
pronoun is used to refer to the object in which the current object is. For
example, referring to 'Parent' in a CommandButton's script will refer to the
window in which the CommandButton is placed. This is used in window control's
scripts and functions. On the other hand, 'ParentWindow' is used to refer to the
window for which the current menu is attached.
Question 110
What
should I do if I want to display an User Object at specific location in a
window dynamically?
Answer
You
can specify the X and Y co-ordinates in the OpenUserObject() and
OpenUserObjectWithParm() functions.
Question 111
Did
you ever use Handle()? Where and How?
Answer
Handle()
function gives the handle number of a given window. In simple terms, it is the
number that identifies a window uniquely. You can use this function to check
whether a particular window is open or not. Especially useful when you want to
check whether another instance of the same application is running or not. You
can use this function along with FindWindow() Windows API call.
Question 112
I
want to find out whether the PowerBuilder application is still connected to the
database or not. What should I do in the PowerScript?
Answer
Use
DbHandle() function.
I
have a window which has a menu associated with. For some reason, I deleted the
menu. Now, I am getting error when I try to open the window. What should I do?
Answer
If
you remember the menu name, just create a dummy menu with the previous menu
name. Now you should be able to open the window. Then, you can de-reference the
menu from the window. If you don't remember the menu name, export the window
and look in the exported file for the menu name. If you know really, you can
edit the exported file and import it back otherwise, just note down the menu
name and follow the first method.
Question 114
There
is a ancestor window 'w_1' with one SingleLineEdit control 'sle_1'. Now, I
created another window 'w_2' by inheriting from the 'w_1' window. In 'w_2' I
changed the window background color to Pink. Then, I went back to 'w_1' and
changed the window background color to Blue and 'sle_1' background color to
Red. What color changes will reflect in 'w-2' window?
Answer
The
thumb rule is that, if you have done any changes to a specific attribute in the
descendent, then any further changes to the same attribute in the ancestor WILL
NOT affect in the descendent. That means, since you have changed the window
background color in the descendent, ancestor's background color change do not
affect the descendent. You haven't changed the background color for the sle_1
in the descendent, So, the background color change for the sle_1 in the
ancestor will reflect in the descendent also.
Question 115
What
are PowerBuilder system tables and how they are useful for a PowerBuilder
programmer?
Answer
There
are five POWERBUILDER system tables, 'PBCatCol', 'PBCatEdt', 'PBCatFmt',
'PBCattbl', 'PBCatVld'. These tables store all the table, column specific
information and POWERBUILDER extended attributes. These tables are created in
the connected database by POWERBUILDER when the first user connects for the
first time. These tables allow you defining extended attributes such as
validation rule, edit style, display style, etc.. Once you create the extended
attributes, these values are by default used when you create a DataWindow,
which will reduce a lot of work and makes dws more consistent.
Question 116
How
do you synchronize Database tables with the PowerBuilder catalog?
Answer
In
the database painter, there is an option to synchronize POWERBUILDER system
tables with actual table/column information.
Question 117
What
is a validation rule? How PowerBuilder validation rule is different from the
Database (validation) rules?
Answer
Validation
rule specifies valid values for a specific column. It allows you to specify
different valid values depending on the content of other columns. Validation
rules defined in POWERBUILDER are used only POWERBUILDER clients. If another
application connects to the database from Excel or Delphi, the database is not
going to validate the data, since, the validation rule is not defined in the
database. Please note that, the validation is done by POWERBUILDER not by the
connected database. On the other hand, if you define the validation rule in the
database, database will validate the value irrespective of the client type. In
this case the validation is done by the connected database not by PowerBuilder.
Explain
different ways of executing a database stored procedure from PowerBuilder.
Answer
You
can source the stored procedure to a DataWindow. You can also execute in the
embedded and dynamic SQL. With version 5.0, you can declare a function for the
stored procedure in the transaction object and execute the stored procedure as
if you are executing a function.
Question 119
What
is a proxy object and what is a remote object?
Answer
Proxy
object represents the remote object in the distributed computing. Whenever you
create a custom class user object, you can specify the proxy name. POWERBUILDER
automatically saves the proxy object whenever you save user object. You place
the actual user object in the server application and keep the proxy object in
the client application. Before you act on the proxy object, you need to call
SetConnect() function to connect to the server object.
Question 120
What
is DDE?
Answer
DDE
means Dynamic Data Exchange. This technology allows two different applications
talk to each other under MS-Windows environment and exchange data between them.
Question 121
List
few DDE related events.
Answer
'HotLinkAlarm',
'RemoteExec', 'RemoteHotlinkStart', 'RemoteHotlinkStop', 'RemoteRequest',
'RemoteSend'.
Question 122
What
is the PowerBuilder object that has DDE related events?
Answer
Window
Question 123
What
is difference between 'Cold Link' and 'Hot Link'?
Answer
In
case of Hot link, the changed data is sent to the client automatically by the
server. In case of 'Cold Link', the changed data is available to the DDE client
only when it requests for that.
Question 124
What
is the difference between 'In-Place editing' and 'Off-site editing'?
Answer
In
case of 'Off-Site Editing', the OLE Server allows you editing in a separate
window other than the OLE client application window. In case of 'In-Place
Editing', the OLE server gets activated in the OLE Client application window
and all the menu options will change accordingly. In this model, user feels
that he is working in a single application even though he is using a different
application.
What
is OCX control? Explain the required steps involved in CREATING an OCX control
in PowerBuilder?
Answer
OCX
is a OLE control which implements the component based architecture. You can use
OCX control in any application that supports OLE 2.0. This increases the object
reusability. You can use the OCX control in POWERBUILDER, but, you can't create
a OCX control in POWERBUILDER in version 5.0.
Question 126
What
is the difference between 'Embedding' and 'Linking' in the OLE context?
Answer
When
you embed an object, the embedded object will be saved as part of the OLE
container object. That means, any future changes to the actual object will not
reflect in the embedded object. This also increases the storage requirement.
Embedded object allows In-Place editing. In case of 'Linking', the original
object resides where it was and a link information is stored in the OLE
container object. That means, any future changes to the actual object will
automatically reflect in the OLE container object. Linked objects are always
invoked for editing off-site.
Question 127
What
is 'AutoInstantiate' and where it is useful?
Answer
The
user object that has 'AutoInstantiate' attribute turned on, will automatically
creates an instance of that object whenever the object is declared. You need to
use the CREATE statement to create the object after declaration when this
property is not set. This attributes is available only for custom class user
objects.
Question 128
What
are the different places you can use OCX control in PowerBuilder?
Answer
You
can use OCX control in a window, in a user object and in a DataWindow.
Question 129
Several
times I heard 'Registry' in the technical meetings. What exactly 'Registry' is?
Answer
Registry
is a MS-Windows database that contains information about each application. The
application populates the information about it self using Windows API calls.
Previously, application specific information such as application preferences,
settings are stored in .INI file which is an ASCII file. Even though there was
registry under MS-Windows 3.x, it wasn't really used by most of the
applications and it was just used to store DDE and OLE specific information.
The data is stored in the registry in the directory like hierarchy format.
Question 130
Explain
the steps required to create a C++ user object in PowerBuilder?
Answer
Basically,
you need to invoke the user object painter for C++ user object type. You need
to declare any instance/shared variables and functions. While declaring
functions, you just declare the function interface, not the function code. You
need to write the actual code for functions in the C++ Editor which comes with
POWERBUILDER. When you save the user object. POWERBUILDER automatically save
the user object as a DLL and you need to deploy this DLL along with your
application.
We
have migrated all our applications from Visual Basic to PowerBuilder. I would
like to use those VBX controls, instead of re-coding in PowerBuilder. Is it
possible? If Yes, are there any restrictions?
Answer
If
you are using POWERBUILDER versions prior to 5.0, you can create a user object
of type VBX and reuse your VBX control. The limitation is that, only Visual
Basic v1.0 specific VBXes are supported by POWERBUILDER. In POWERBUILDER 5.0,
you can't use VBX any more. Actually, it would be better stop using VBX and
migrate to OCX which allows deploying your applications in 32-bit environment.
Question 132
The
OCX control I planned to use has a 'Clicked' event. The OLE 2.0 control in
PowerBuilder already has 'Clicked' event. What should I do?
Answer
When
you are in the design mode, delete the duplicate events by selecting
'Declare/User Events' from the menu. This will solve the run-time problems.
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