ORACLE PLSQL

21. Write the order of precedence for validation of a column in a table?

I. Validation is done using Database triggers.
II. Validation is done using Integrity Constraints.

22. What is an Exception? What are types of Exception?

Exception is the error handling part of PL/SQL block
The types are Predefined and user defined.
Some of Predefined exceptions are.
CURSOR_ALREADY_OPEN, DUP_VAL_ON_INDEX, NO_DATA_FOUND, TOO_MANY_ROWS,
INVALID_CURSOR, INVALID_NUMBER, LOGON_DENIED, NOT_LOGGED_ON,
PROGRAM-ERROR,
STORAGE_ERROR, TIMEOUT_ON_RESOURCE, VALUE_ERROR, ZERO_DIVIDE, OTHERS.

23. What is Pragma EXECPTION_INIT? Explain the usage?

The PRAGMA EXECPTION_INIT tells the complier to associate an exception with an oracle error.
To get an error message of a specific oracle error.
E.g. PRAGMA EXCEPTION_INIT (exception name, oracle error number)

24. What is Raise_application_error ?

Raise_application_error is a procedure of package DBMS_STANDARD which allows to issue an user_defined error messages from stored sub-program or database trigger.

25. What are the return values of functions SQLCODE and SQLERRM?

SQLCODE returns the latest code of the error that has occurred.
SQLERRM returns the relevant error message of the SQLCODE.

26. Where the Pre_defined_exceptions are stored?

In the standard package.

27. What is a stored procedure?

A stored procedure is a sequence of statements that performs specific function.

28. What is difference between a PROCEDURE & FUNCTION?

A FUNCTION is always returns a value using the return statement.
A PROCEDURE may return one or more values through parameters or may not return at all.


29. What are the advantages of Stored Procedures?

Extensibility, Modularity, Reusability, Maintainability and one time compilation.

30. What are the modes of parameters that can be passed to a procedure?

IN, OUT, IN-OUT parameters.

31. What are the two parts of a procedure?

Procedure Specification and Procedure Body.

32. Give the structure of the procedure?

PROCEDURE name (parameter list...) is local variable declarations
BEGIN
Executable statements.
Exception.
exception handlers
end;

33. Give the structure of the function?

FUNCTION name (argument list...) Return data type is local variable declarations
Begin
executable statements
Exception
execution handlers
End;

34. Explain how procedures and functions are called in a PL/SQL block?

Function is called as part of an expression.
sal := calculate_sal ('a822');
procedure is called as a PL/SQL statement
calculate_bonus ('A822');

35. What is Overloading of procedures?

The Same procedure name is repeated with parameters of different data types and parameters in different positions, varying number of parameters is called overloading of procedures.

Ex. DBMS_OUTPUT put_line

36. What is a package? What are the advantages of packages?

Package is a database object that groups logically related procedures. The advantages of packages are Modularity, Easier Application Design, and Information hiding, Reusability and Better Performance.



37.What are two parts of package?

The two parts of package are PACKAGE SPECIFICATION & PACKAGE BODY.
Package Specification contains declarations that are global to the packages and local to the schema.
Package Body contains actual procedures and local declaration of the procedures and cursor declarations.

38. What is difference between a Cursor declared in a procedure and Cursor declared in a package specification?

A cursor declared in a package specification is global and can be accessed by other procedures or procedures in a package.
A cursor declared in a procedure is local to the procedure that cannot be accessed by other procedures.

39. How packaged procedures and functions are called from the following?
a. Stored procedure or anonymous block
b. An application program such a PRC *C, PRO* COBOL
c. SQL *PLUS

a. PACKAGE NAME.PROCEDURE NAME (parameters);
variable := PACKAGE NAME.FUNCTION NAME (arguments);
EXEC SQL EXECUTE
b. BEGIN
PACKAGE NAME.PROCEDURE NAME (parameters)
variable := PACKAGE NAME.FUNCTION NAME (arguments);
END;
END EXEC;
c. EXECUTE PACKAGE NAME.PROCEDURE if the procedures does not have any
out/in-out parameters. A function can not be called.

40. Name the tables where characteristics of Package, procedure and functions are stored?

User_objects, User_Source and User_error.

41. What is a View? Why is it required to define a View?

A View is a database object that is a logical representation of a table. It is derived from a table but has no storage space of its own and often may be used in the same manner as a table.
Advantage:
Security
Complex query can be replaced.

42. Can we create a View without a table?

Yes, Using the FORCE option in the CREATE VIEW
Syntax:
Ex: CREATE FORCE VIEW view_name as SELECT columnname,columnname
FROM table_name;
43. What is the difference between SYNONYM and VIEW?

A SYNONYM is a name assigned to a table or view that may thereafter be used to refer it. If you access to another user’s table, you may create a synonym for it and refer to it by the synonym alone, without entering the user’s name as a qualifier.

A View is a database object that is a logical representation of a table. It is derived from a table but has no storage space of its own and often may be used in the same manner as a table.
Difference: A View can be based on MULTIPLE Tables whereas a SYNONYM is based on a single object only.

44. What is SNAPSHOT? What is a SNAPSHOT LOG?

A SNAPSHOT is a means of creating a local copy of remote data. A snapshot can be used to replicate all or part of a single table, or to replicate the result of a query against multiple tables. The refreshes of the replicated data can be done automatically by the database ( at time intervals you specify ) or manually.
Snapshot Log is the table associated with the Master Table of the Snap shot.

45. What is a DATABASE trigger? What is a DATABASE Procedure?

A DATABASE TRIGGER is a stored procedure associated with a table that ORACLE7 automatically executes on one or more specified events (BEFORE or AFTER an INSERT, UPDATE or DELETE) affecting the table. Triggers can execute for the table as a whole or for each affected row in the table.
A PACKAGED PROCEDURE is a built-in PL/SQL procedure that is available in all forms. Each packaged procedure executes a SQL*FORMS function, such as moving to a field or executing a query.

46. How to show MESSAGES in PROCEDURES for debugging purposes?

DBMS_OUTPUT_PACKAGE allows you to use three debugging functions within your package. You must use “SET SERVER OUTPUT ON” before executing the procedure object you will be debugging.
PUT Puts multiple O/P’s on same line.
PUT_LINE Puts each O/P on a separate line.
NEW_LINE Used with PUT; Signals the end of current O/P line.

47. What is the difference between DATABASE trigger and DATABASE procedure?

DATABASE triggers are executed automatically in response to specific events.
But the DATABASE procedures are to be explicitly invoked to execute the code contained in them.

48. Is there a limit on the size of a PL/SQL block?

Currently, the maximum parsed/compiled size of a PL/SQL block is 64K and the maximum code size is 100K. You can run the following select statement to query the size of an existing package or procedure. SELECT * FROM DBA_OBJECT_SIZE WHERE NAME = 'PROCEDURE NAME'
A table exists with 3 columns C1 ,C2 & C3.

49. What are the attributes of IMPLICIT CURSOR?

%ISOPEN, %ROWCOUNT, %FOUND and %NOTFOUND.

Attribute DML STATEMENT RETURNS ROW RETURNS NO ROW

%ISOPEN FALSE FALSE

%ROWCOUNT TRUE FALSE ( ZERO )

%FOUND TRUE FALSE

%NOTFOUND FALSE TRUE

50. Can we pass a PARAMETER to CURSOR? What is SQL%ROWCOUNT?

We can pass parameter to CURSOR. Eg: OPEN CURSOR(‘VASAN’).
SQL%ROWCOUNT is used to count the number of rows returned by an SQL DML
statement.It will return zero if the DML statement doesn’t return any row.