Friday, October 18, 2013

SQL, PL/SQL FAQs





About Triggers:
1.    What is triggers?  What are the different types of triggers?
      
A database trigger is a stored subprogram associated with a database table, view, or event. For instance, you can have Oracle fire a trigger automatically before or after
an INSERT, UPDATE, or DELETE statement affects a table.

A Database Trigger is a stored procedure that is fired when a DML operation is performed on the table. In total there are 13 types of Triggers
Syntax for creating a trigger:
   CREATE OR REPLACE TRIGGER <TRIGGERNAME> before / after
          [INSERT / UPDATE / DELETE ] ON <TABLE NAME>
          {For each Statement / Row}
          {When <condition…..>}
Types of Triggers:
Before
After
For each Row
For each Statement (default)
Instead of Trigger: This trigger is defined on a view rather than a table.

System Triggers: A new feature of Oracle8i, wherein the trigger is fired when the database startup / shutdown process.

Schema Triggers: These triggers are fired whenever a DDL statement is executed.  (Creation or Deletion of any DB Objects)

Order of Trigger Firing:
·       Before Statement trigger (If present)
·       Each row affected by the statement
(a) Execute row level trigger (If present)
(b)  Execute the statement itself
(c) Execute the after row level trigger (If Present)
·       After statement trigger (If Present)

2.    What are the different types of joins available in Oracle?
Equi Join: When primary and foreign key relationship exists between the tables that are going to be joined.
Self Join: If comparison comes in a single table
Cartesian Join: When tables are joined without giving any join condition.
Inner Join: The resultant set includes all the rows that satisfy the join condition.
Outer Join: The resultant set includes the rows which doesn’t satisfy the join condition.  The outer join operator Plus sign (+) will be included in the join condition.
Example: SELECT a. column1, a. column2, b.column3….. From a, b where
a.column1 (+) =b.Column1
Here the rows from table which doesn’t satisfy the join condition will also be fetched.


3.    What are Indexes?  What are the different types of Index? If a table consists of more than one Index how to enforce the statement to use the second Index?

An Index is a DB object, which is used to improve the performance of  the data retrieval.
CREATE INDEX <INDEX NAME> ON <TABLE name>.(<COLUMN name>)
Types of Indexes:
Bitmap Index (Used for Low cardinality column)
Btree Index (Used for high cardinality column)
Note: It is not possible to crea

4.    What is Mutating Table?
Table under transition is called Mutating Table. 

5.    What is views?  What is Inline View??
Views are window to a table.  It contains no data, it is based on the actual table called the base table or a view.
Inline View means writing select statement in the Query itself instead of selecting a Column Name.

6.    What is a Cursor?  When it is used?   What are different types of Cursors.
Cursor is a private SQL area created in SGA to do multi row operation in a PL/SQL programme
Explicit Cursor, Implicit Cursor.
Implicit Cursor: System (Oracle) automatically declares and uses for all DML SQL Statements.
Explicit Cursor: Cursor declared explicitly in the PL/SQL programme to do multi row operation
Syntax:
Declare
Cursor C1 is SELECT SAL, EMPNO FROM EMP
X number;
Y Varchar2(30);
Begin
         Open C1;
            Loop
   Fetch C1 INTO x, y;
            Exit when c1%NOTFOUND
            End Loop;
End;

7.    What is for Cursor?  When it is used?  Is it necessary to write an explicit exit in case for Cursor?
A Cursor for loop can be used simplify the explicit cursor, no need to explicitly Open, fetch and close.  No explicity EXIT statement is required.

8.    What are Cursor attributes? What is use of FOR UPDATE in Cursor?
%Found
%NotFound
%RowCount
%IsOpen
     
FOR UPDATE statement in Cursor is used to update a Column in the selected table by using the CURRENT OF <cursor name>.

9.    What is a Package?  What is the advantage of using Packages?
A Package is a PL/SQL Construct that allow related object to be stored together.  Package contains 2 parts, Package Specification and Package Body, each stored separately in the Data Dicitionary.
Once the Package is called all the related Procedure and functions of the package gets compiled and stored in the memory as P-code.
How do u call a Package.
<PackageName>.<Procedure / Function Name> (Related Parameters….)

10.       Name some important Packages provided by Oracle?
DBMS_SQL, DBMS_JOBS, DBMS_DDL, DBMS_LOCK

11.       What is Overloading?
Overloading is oops concept(Object Oriented Programming)
By Using the same name we can write any number of Procedure or functions in a package but either number of parameters in the procedure/function must be vary or parameter datatype must vary.

12.       What is a Function?   Difference between Procedure and Function?
Function is a object that takes one or more arguments and returns only value. But in case of procedures we can return more than one parameters.
Function always returns a value, whereas procedure may or may not return a value.


13.       What is the Package used in Oracle to do the File Operation?
UTL_FILE

14.       What is Dynamic SQL?  How Dynamic SQL can be built?
The SQL statement which are built at run time are called the Dynamic SQL.  Dynamic SQL can be built by using DBMS_SQL package.
Procedure of Dynamic SQL
OPEN_CURSOR, PARSE, BIND_VARIABLE, DEFINE_COLUMN, EXECUTE, FETCH_ROWS, CLOSE_CURSOR.
Oracle8i onwards there is another built in to construct Dynamic SQL called EXECUTE_IMMEDIATE.


15.       What is an exception?  What are the different types of Exception?  How do u
declare a user defined exception?
The error condition in PL/SQL  is termed as an exception.  Two types of
Exception:
Pre-Defined Exception: Example No_Data_Found, Storage_Error,
Zero_Error, Invlid_Cursor, Too_Many_Rows
User-Defined Exception: Anything

Syntax:
Declare
Xyz Exception;
Begin
   SELECT ENAME FROM EMP
   RAISE XYZ;
End;

16.       what could happen if we use WHEN OTHERS before any predefined exceptions
According to the Oracle standards “ When Others “ exception must be the last exception. All the Predefined exceptions must be used before the “When others” exception.
            If “ When others” exception used before any pre-defined exceptions then  procedure/function shows the compilations errors
   
17.       List out some features in 8i
Bitmap Indexes, Drop a Column, Bulk Insert and Bulk Update
Materialized views, Dynamic Sql(Execute Immediate etc)
     
18.       List some 9iFeatures
External tables ( We query the data directly from a file like select * from “c:/abcd.csv” )
Multi Table Insert with single command, resumable process etc.
     
19.       What are SQLCODE and SQLERRM and why are they important for PL/SQL 
           developers?

SQLCODE returns the value of the error number for the last error encountered. The SQLERRM returns the actual error message for the last error encountered. They can be used in exception handling to report, or, store in an error log table, the error that occurred in the code. These are especially useful for the WHEN OTHERS exception

20.       What is the use of Pragma_Init exception
By using this we can define our messages by handling the oracle messages

21.       What are temporary tables? How many types?
Temporary tables are used to store the data temporarly. Mainly there are 2 types
They are transaction and Session types
Syntax: Create global temporary table <temp_tab> as select * from emp;
This temporarly table is used to store the data temparorly once you exit from session then that table will get erased
22.       Some of the System Tables
a.     User_source table will stores the information of the user defined definitions
b.    All_Source and dba_source tables will stores the system defined schema objects definitions as well as user defined.
c.     All_Tab_Columns and ben_all_tab_columns are used to list  out the all the columns name and respected table names also.

23.       Write a query to list out the employees with their respective manager levels?

select lpad('*', level * 2), empno, ename, mgr from emp
connect by prior empno = mgr start with empno = 7839
It results the hierarchy of the employees
 Note : For Answers Check the Next Page

* What is PL/SQL and what is it used for?
* Should one use PL/SQL or Java to code procedures and triggers?
* How can one see if somebody modified any code?
* How can one search PL/SQL code for a key?
* How can one keep a history of PL/SQL code changes?
* How can I protect my PL/SQL source code?
* Can one print to the screen from PL/SQL?
* Can one read/write files from PL/SQL?
* Can one call DDL statements from PL/SQL?
* Can one use dynamic SQL statements from PL/SQL?
* What is the difference between %TYPE and %ROWTYPE?
* How does one get the value of a sequence into a PL/SQL variable?
* Can one execute an operating system command from PL/SQL?
* How does one loop through tables in PL/SQL?
* How often should one COMMIT in a PL/SQL loop? / What is the best commit strategy?
* I can SELECT from SQL*Plus but not from PL/SQL. What is wrong?
* What is a mutating and constraining table?
* Can one pass an object/table as an argument to a remote procedure?
* Is it better to put code in triggers or procedures? What is the difference?
* Is there a PL/SQL Engine in SQL*Plus?
* Is there a limit on the size of a PL/SQL block?
* Where can one find more info about PL/SQL?

What is PL/SQL and what is it used for?

PL/SQL is Oracle's Procedural Language extension to SQL. PL/SQL's language syntax, structure and data types are similar to that of ADA. The PL/SQL language includes object oriented programming techniques such as encapsulation, function overloading, information hiding (all but inheritance). PL/SQL is commonly used to write data-centric programs to manipulate data in an Oracle database.

Should one use PL/SQL or Java to code procedures and triggers?

Internally the Oracle database supports two procedural languages, namely PL/SQL and Java. This leads to questions like "Which of the two is the best?" and "Will Oracle ever desupport PL/SQL in favour of Java?".
Many Oracle applications are based on PL/SQL and it would be difficult of Oracle to ever desupport PL/SQL. In fact, all indications are that PL/SQL still has a bright future ahead of it. Many enhancements are still being made to PL/SQL. For example, Oracle 9iDB supports native compilation of Pl/SQL code to binaries.

PL/SQL and Java appeal to different people in different job roles. The following table briefly describes the difference between these two language environments:

PL/SQL:

Data centric and tightly integrated into the database
Proprietary to Oracle and difficult to port to other database systems
Data manupilation is slightly faster in PL/SQL than in Java
Easier to use than Java (depending on your background)
Java:

Open standard, not proprietary to Oracle
Incurs some data conversion overhead between the Database and Java type systems
Java is more difficult to use (depending on your background)

How can one see if somebody modified any code?

Code for stored procedures, functions and packages is stored in the Oracle Data Dictionary. One can detect code changes by looking at the LAST_DDL_TIME column in the USER_OBJECTS dictionary view. Example:
        SELECT OBJECT_NAME,
               TO_CHAR(CREATED,       'DD-Mon-RR HH24:MI') CREATE_TIME,
               TO_CHAR(LAST_DDL_TIME, 'DD-Mon-RR HH24:MI') MOD_TIME,
               STATUS
        FROM   USER_OBJECTS
        WHERE  LAST_DDL_TIME > '&CHECK_FROM_DATE';

How can one search PL/SQL code for a key?

The following query is handy if you want to know where a certain table, field or expression is referenced in your PL/SQL source code.
        SELECT TYPE, NAME, LINE
        FROM   USER_SOURCE
        WHERE  UPPER(TEXT) LIKE '%&KEYWORD%';

* By useing DBA_DEPENDENCIES table you can find out. - Ezhil

How can one keep a history of PL/SQL code changes?

One can build a history of PL/SQL code changes by setting up an AFTER CREATE schema (or database) level trigger (available from Oracle 8.1.7). This way one can easily revert to previous code should someone make any catastrophic changes. Look at this example:
        CREATE TABLE SOURCE_HIST                     -- Create history table
          AS SELECT SYSDATE CHANGE_DATE, USER_SOURCE.*
             FROM   USER_SOURCE WHERE 1=2;

        CREATE OR REPLACE TRIGGER change_hist        -- Store code in hist table
               AFTER CREATE ON SCOTT.SCHEMA          -- Change SCOTT to your schema name
        DECLARE
        BEGIN
          if DICTIONARY_OBJ_TYPE in ('PROCEDURE', 'FUNCTION',
                          'PACKAGE', 'PACKAGE BODY', 'TYPE') then
             -- Store old code in SOURCE_HIST table
             INSERT INTO SOURCE_HIST
                SELECT sysdate, user_source.* FROM USER_SOURCE
                WHERE TYPE = DICTIONARY_OBJ_TYPE
                  AND NAME = DICTIONARY_OBJ_NAME;
          end if;
        EXCEPTION
          WHEN OTHERS THEN
               raise_application_error (-20000, SQLERRM);
        END;
        /
        show errors

How can I protect my PL/SQL source code?

PL/SQL V2.2, available with Oracle7.2, implements a binary wrapper for PL/SQL programs to protect the source code.
This is done via a standalone utility that transforms the PL/SQL source code into portable binary object code (somewhat larger than the original). This way you can distribute software without having to worry about exposing your

proprietary algorithms and methods. SQL*Plus and SQL*DBA will still understand and know how to execute such scripts. Just be careful, there is no "decode" command available.

The syntax is:

      wrap iname=myscript.sql oname=xxxx.plb


Can one print to the screen from PL/SQL?

One can use the DBMS_OUTPUT package to write information to an output buffer. This buffer can be displayed on the screen from SQL*Plus if you issue the SET SERVEROUTPUT ON; command. For example:
      set serveroutput on

      begin
         dbms_output.put_line('Look Ma, I can print from PL/SQL!!!');
      end;
      /

DBMS_OUTPUT is useful for debugging PL/SQL programs. However, if you print too much, the output buffer will overflow. In that case, set the buffer size to a larger value, eg.: set serveroutput on size 200000

If you forget to set serveroutput on type SET SERVEROUTPUT ON once you remember, and then EXEC NULL;. If you haven't cleared the DBMS_OUTPUT buffer with the disable or enable procedure, SQL*Plus will display the entire contents of the buffer when it executes this dummy PL/SQL block.


Can one read/write files from PL/SQL?

Included in Oracle 7.3 is an UTL_FILE package that can read and write operating system files. The directory you intend writing to has to be in your INIT.ORA file (see UTL_FILE_DIR=... parameter). Before Oracle 7.3 the only means of writing a file was to use DBMS_OUTPUT with the SQL*Plus SPOOL command.
Copy this example to get started:

      DECLARE
        fileHandler UTL_FILE.FILE_TYPE;
      BEGIN
        fileHandler := UTL_FILE.FOPEN('/tmp', 'myfile', 'w');
        UTL_FILE.PUTF(fileHandler, 'Look ma, I''m writing to a file!!!\n');
        UTL_FILE.FCLOSE(fileHandler);
      EXCEPTION
        WHEN utl_file.invalid_path THEN
           raise_application_error(-20000, 'ERROR: Invalid path for file or path not in INIT.ORA.');
      END;
      /

Can one call DDL statements from PL/SQL?

One can call DDL statements like CREATE, DROP, TRUNCATE, etc. from PL/SQL by using the "EXECUTE IMMEDATE" statement. Users running Oracle versions below 8i can look at the DBMS_SQL package (see FAQ about Dynamic SQL).
      begin
         EXECUTE IMMEDIATE 'CREATE TABLE X(A DATE)';
      end;

NOTE: The DDL statement in quotes should not be terminated with a semicolon.

Can one use dynamic SQL statements from PL/SQL?

From PL/SQL V2.1 one can use the DBMS_SQL package to execute dynamic SQL statements. Eg:
      CREATE OR REPLACE PROCEDURE DYNSQL AS
        cur integer;
        rc  integer;
      BEGIN
        cur := DBMS_SQL.OPEN_CURSOR;
        DBMS_SQL.PARSE(cur, 'CREATE TABLE X (Y DATE)', DBMS_SQL.NATIVE);
        rc := DBMS_SQL.EXECUTE(cur);
        DBMS_SQL.CLOSE_CURSOR(cur);
      END;
      /

Another example:
      CREATE OR REPLACE PROCEDURE DEPARTMENTS(NO IN DEPT.DEPTNO%TYPE) AS
        v_cursor integer;
        v_dname  char(20);
        v_rows   integer;
      BEGIN
        v_cursor := DBMS_SQL.OPEN_CURSOR;
        DBMS_SQL.PARSE(v_cursor, 'select dname from dept where deptno > :x', DBMS_SQL.V7);
        DBMS_SQL.BIND_VARIABLE(v_cursor, ':x', no);
        DBMS_SQL.DEFINE_COLUMN_CHAR(v_cursor, 1, v_dname, 20);
        v_rows := DBMS_SQL.EXECUTE(v_cursor);
        loop
          if DBMS_SQL.FETCH_ROWS(v_cursor) = 0 then
             exit;
          end if;
          DBMS_SQL.COLUMN_VALUE_CHAR(v_cursor, 1, v_dname);
          DBMS_OUTPUT.PUT_LINE('Deptartment name: '||v_dname);
        end loop;
        DBMS_SQL.CLOSE_CURSOR(v_cursor);
      EXCEPTION
        when others then
             DBMS_SQL.CLOSE_CURSOR(v_cursor);
             raise_application_error(-20000, 'Unknown Exception Raised: '||sqlcode||' '||sqlerrm);
      END;
      /

What is the difference between %TYPE and %ROWTYPE?

The %TYPE and %ROWTYPE constructs provide data independence, reduces maintenance costs, and allows programs to adapt as the database changes to meet new business needs.
%ROWTYPE is used to declare a record with the same types as found in the specified database table, view or cursor. Example:

      DECLARE
         v_EmpRecord  emp%ROWTYPE;
%TYPE is used to declare a field with the same type as that of a specified table's column. Example:

      DECLARE
         v_EmpNo  emp.empno%TYPE;

How does one get the value of a sequence into a PL/SQL variable?

As you might know, oracle prohibits this:
      i := sq_sequence.NEXTVAL;
(for some silly reason). But you can do this:
      select sq_sequence.NEXTVAL into :i from dual;
Thanks to Ronald van Woensel

Can one execute an operating system command from PL/SQL?

There is no direct way to execute operating system commands from PL/SQL in Oracle7. However, one can write an external program (using one of the precompiler languages, OCI or Perl with Oracle access modules) to act as a listener on a database pipe (SYS.DBMS_PIPE). Your PL/SQL program then put requests to run commands in the pipe, the listener picks it up and run the requests. Results are passed back on a different database pipe. For an Pro*C example, see chapter 8 of the Oracle Application Developers Guide.
In Oracle8 one can call external 3GL code in a dynamically linked library (DLL or shared object). One just write a library in C/ C++ to do whatever is required. Defining this C/C++ function to PL/SQL makes it executable. Look at this External Procedure example.


How does one loop through tables in PL/SQL?

Look at the following nested loop code example.
      DECLARE
         CURSOR dept_cur IS
         SELECT deptno
           FROM dept
          ORDER BY deptno;
         -- Employee cursor all employees for a dept number
         CURSOR emp_cur (v_dept_no DEPT.DEPTNO%TYPE) IS
         SELECT ename
           FROM emp
          WHERE deptno = v_dept_no;
      BEGIN
         FOR dept_rec IN dept_cur LOOP
            dbms_output.put_line('Employees in Department '||TO_CHAR(dept_rec.deptno));
            FOR emp_rec in emp_cur(dept_rec.deptno) LOOP
               dbms_output.put_line('...Employee is '||emp_rec.ename);
            END LOOP;
        END LOOP;
      END;
      /

How often should one COMMIT in a PL/SQL loop? / What is the best commit strategy?

Contrary to popular believe, one should COMMIT less frequently within a PL/SQL loop to prevent ORA-1555 (Snapshot too old) errors. The higher the frequency of commit, the sooner the extents in the rollback segments will be cleared for new transactions, causing ORA-1555 errors.
To fix this problem one can easily rewrite code like this:

      FOR records IN my_cursor LOOP
         ...do some stuff...
         COMMIT;
      END LOOP;

... to ...
      FOR records IN my_cursor LOOP
         ...do some stuff...
         i := i+1;
         IF mod(i, 10000) THEN    -- Commit every 10000 records
            COMMIT;
         END IF;
      END LOOP;

If you still get ORA-1555 errors, contact your DBA to increase the rollback segments.
NOTE: Although fetching across COMMITs work with Oracle, is not supported by the ANSI standard.

I can SELECT from SQL*Plus but not from PL/SQL. What is wrong?

PL/SQL respect object privileges given directly to the user, but does not observe privileges given through roles. The consequence is that a SQL statement can work in SQL*Plus, but will give an error in PL/SQL. Choose one of the following solutions:
Grant direct access on the tables to your user. Do not use roles!
      GRANT select ON scott.emp TO my_user;
   
Define your procedures with invoker rights (Oracle 8i and higher);

Move all the tables to one user/schema.

What is a mutating and constraining table?

"Mutating" means "changing". A mutating table is a table that is currently being modified by an update, delete, or insert statement. When a trigger tries to reference a table that is in state of flux (being changed), it is considered "mutating" and raises an error since Oracle should not return data that has not yet reached its final state.
Another way this error can occur is if the trigger has statements to change the primary, foreign or unique key columns of the table off which it fires. If you must have triggers on tables that have referential constraints, the workaround is to enforce the referential integrity through triggers as well.

There are several restrictions in Oracle regarding triggers:

A row-level trigger cannot query or modify a mutating table. (Of course, NEW and OLD still can be accessed by the trigger) .
A statement-level trigger cannot query or modify a mutating table if the trigger is fired as the result of a CASCADE delete.
Etc.

Can one pass an object/table as an argument to a remote procedure?

The only way the same object type can be referenced between two databases is via a database link. Note that it is not enough to just use the same type definitions. Look at this example:
      -- Database A: receives a PL/SQL table from database B
      CREATE OR REPLACE PROCEDURE pcalled(TabX DBMS_SQL.VARCHAR2S) IS
      BEGIN
         -- do something with TabX from database B
         null;
      END;
      /

      -- Database B: sends a PL/SQL table to database A
      CREATE OR REPLACE PROCEDURE pcalling IS
         TabX DBMS_SQL.VARCHAR2S@DBLINK2;
      BEGIN
         pcalled@DBLINK2(TabX);
      END;
      /

Is it better to put code in triggers or procedures? What is the difference?

In earlier releases of Oracle it was better to put as much code as possible in procedures rather than triggers. At that stage procedures executed faster than triggers as triggers had to be re-compiled every time before executed (unless cached). In more recent releases both triggers and procedures are compiled when created (stored p-code) and one can add as much code as one likes in either procedures or triggers.

Is there a PL/SQL Engine in SQL*Plus?

No. Unlike Oracle Forms, SQL*Plus does not have a PL/SQL engine. Thus, all your PL/SQL is sent directly to the database engine for execution. This makes it much more efficient as SQL statements are not stripped off and sent to the database individually.

Is there a limit on the size of a PL/SQL block?
Yes, the max size is not an explicit byte limit, but related to the parse tree that is created when you compile the code. You can run the following select statement to query the size of an existing package or procedure:
      SQL> select * from dba_object_size where name = 'procedure_name';




                                                 Forms/Reports

1. How you declare global variables in forms ?
    Global variable will declared in When-New-Form-Instance Triggers

2. What are Table Handlers and Event Handlers?

3. What are new feature in forms 6i compared to forms4.5

4.What is the Difference between callform, Newform, Openform

5.What is the Use of Program Units in form/reports ?

6.How many triggers is there in reports and what are they and what is the Order of firing
Before Parameter Form
After Parameter Form
Before report
Between pages
After Report

7.Which trigger will get fired while opening an LOV in forms
   Key-List-Value

8. How Many Types of reports are there? Name it??

9. What is the Use of Anchors in Reports

10. What is the uses and differences between Summary Column, Formula column and Place holder   column?

11. What is the Difference between Bind parameter  and lexical parameter? Which trigger will be used to specify the conditions for a lexical parameter.

12. What is the use of Destype, Desname, Desformat in Parameter form.

13.When the Between Pages Trigger will fire?
      After first page this trigger will fire until last  
      page and after that for last page it wont fire.


14. What are the form Modules?
       They are 4 types of form modules are there 1) Alerts 2) Forms Modules 3) Menu
       Modules 4) PLSQL Libraries

15.Some of the New Features in Reports6i
   In 6i we can generate the report in different types like PDF,HTML,XML, RTF etc
   In reports goto -> Layout model à Header or Body or Margin sections à property  
   Pallateà Distributions. Specify the Type and file name with path.
   Then gotoà File à Distribute.

16. What is the difference between Format Triggers and Action Triggers
     Action Trigger is Procedure whereas Format Trigger is Procedure
     By using Action trigger we can open the other form or report

17 What is the Difference between FlexMode and Confine Mode and their differences

18. What is the Order of triggers firing
       W-N-F-I, Pre-Form, W-N-I-I, W-N-B-I ??

19 What is the Major Differences and uses between Property Class and Visual Attribute

20. Other than Run_Product how can we run a report from a form
   By using  Run_Report_Object function we can run the reports( This is 6i New Feature)
   To use this Add that report in Form Object Navigator and pass the Id of that report.

21. What are the Default triggers will be created when a master-detail form is created
 There are 3 types are triggers will be created in form level when a master-detail form is   
 created.
22. What is the Diiference between .pll, .pls and .plx in Libraries

23. What is Object Library and Attached Library
      Object Library can be used to stored Function, Procedure, Package. Attached library will be used to avoid any change in source code. Object library can be converted into .PLX and attached to Attache library.

24  What is the difference between writing code in Programme Unit and Library Files?
      The code written in Programme unit is form’s specific, whereas code written in
     Library files, can be used across the forms.

25.   When a form is run, which are the triggers fire, and in what sequence they fire?
PRE-FORM
WHEN-NEW-FORM-INSTANCE
PRE-BLOCK
WHEN-NEW-BLOCK-INSTANCE
WHEN-NEW-ITEM-INSTANCE
POST-BLOCK
POST-FORM

1.    What is the difference between Forms 4.5 and Forms 6i
Tab Page utility is not available in 4.5 Version

2.    What is the utility used to call the report from the forms?
RUN_REPORT

3.    What is a Property Class? Different methods of creating property class?
Property Class is defining properties of objects along with their settings.  The property class inheritance allows the user to perform global changes very quickly and efficiently.
Methods:
Object Navigator Method
Properties Window Method

4.    WHEN-NEW-FORM trigger written at Form Level, Block Level and Item Level
which one will fire first?
The trigger written at the lower level Item Level Fires first then at Block Level and at last it fires in Form Level.

5.    In the previous question circumstance, is it possible to change the order of trigger
Execution?  If Yes, where it needs to be changed?
Yes, in the trigger property (Before, After, Default)by changing the attributes.

6.    What are the different kinds of Parameters available in the report?
           System and User defined Parameters.(Bind and Lexical Parameters)


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