About Triggers:
1. What is triggers? What are the different types of triggers?
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
Sytax for creating a trigger:
CREATE OR REPLACE TRIGGER
[INSERT / UPDATE / DELTE ] ON {For each Statement / Row} {When
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 using 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_list -- Store code in list 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 Header or Body or Margin sections property
Pallate Distributions. Specify the Type and file name with path.
Then goto File 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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