CBSE Book Class 12 Informatics Practices Tables And Exception Propagation

Chapter – 3

Tables And Exception Propagation

(Informatics Practices)

PL/SQl TABLEs combine characteristics of SQL tables and C/Pascal arrays.

Like SQL tables:

• consist of records (must have a numeric primary key)
• can grow/shrink as elements are added/removed

Exceptions

An exception is an unusual/erroneous condition encountered during execution:

• system error (e.g. "out of memory")
• error caused by user program
• warning issued by application

PL/SQL's exception handling allows these to be handled "cleanly" in a central place.

Syntax for exception handlers:

BEGIN

... Statements ...

EXCEPTION

WHEN ExcepName1 THEN Statements1;

WHEN ExcepName2 THEN Statements2;

...

END;

If an error occurs in Statements, control is transferred to:

• the exception handler in this block
• the exception handler at the next enclosing block
• ... and so on out to the system level

Example: Computing stock-market price/earnings ratio

DECLARE

       pe_ratio NUMBER(5,1);

BEGIN

     SELECT price/earnings INTO pe_ratio

     FROM StocksWHERE company_name = 'Acme';

    INSERT INTO Statistics(co_name, ratio)

        VALUES ('Acme', pe_ratio);

   COMMIT;

EXCEPTION

   WHEN ZERO_DIVIDE THEN -- divide-by-zero errors

   INSERT INTO Statistics(co_name, ratio)

       VALUES ('Acme', 0.0);

-- other exception handlers

END;

Please refer to attached file for CBSE Classs 12 Informatics Practices Tables And Exception Propagation