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NULL Statement
The NULL statement clearly specifies in action; it does nothing other than to pass control to the next statement. It can, though, improve the readability. In a construct allowing the substitute actions, the NULL statements serve as a placeholder. It tells the readers that the related alternative has not been overlooked, but required that no action is necessary. In the following illustration, the NULL statement shows that no action is taken for the unnamed exceptions:EXCEPTIONWHEN ZERO_DIVIDE THENROLLBACK;WHEN VALUE_ERROR THENINSERT INTO errors VALUES...COMMIT;WHEN OTHERS THENNULL;END;Each of the clause in an IF statement should contain at least one executable statement. TheNULL statement is executable; therefore you can use it in clauses that correspond to the circumstances in which no action is taken. In the following illustration, the NULL statements emphasize that only top-rated employees get bonus:IF rating > 90 THENcompute_bonus(emp_id);ELSENULL;END IF;The NULL statement is also a handy way to create stubs when designing the applications from the top down. A stub is dummy subprogram that permits you to defer the definition of a procedure or function till you test and debug the main program. In the following illustration, the NULL statement meets the requirement that at least one statement should appear in the executable part of a subprogram:PROCEDURE debit_account (acct_id INTEGER, amount REAL) ISBEGINNULL;END debit_account;
TTITLE and BTITLE are commands in Pl-SQL to control report headings and footers. This Ttitle & Btitle are mainly used on creating SQL*PLUS report. Ttitle is used for toptitle headi
Parameter Modes: You do not require to specify a parameter mode for the input bind arguments (those used, for illustration, in the WHERE clause) as the mode defaults to IN. Th
Initializing and Referencing Collections Until you initialize a collection, a nested table or varray is automatically null (i.e. the collection itself is null, not its elements)
Pl/sql Conditional Control: IF statements Frequently, it is necessary to take the alternative actions depending on the circumstances. The IF statement execute a series of statem
Creating a SQL file 1. Open a new file in Notepad++ and save it to the location c:\mysql\bin, with the name lab8script.sql (the file extension should be .sql ). Add a MySQL co
Declarations in SQL Your program stores values in the variables and constants. As the program executes, the value of the variables can change, but the values constants cannot.
Example of EXCEPT Operator - SQL Example, like its counterpart in the theory book, illustrates the convenience of allowing any table expression to be the source for an INSERT
Raise_application_error - procedure of package DBMS_STANDARD , allows to issue an user_defined error messages by stored sub-program or database trigger.
Effects of NULL The numeric variable X, perhaps of type INTEGER, might be assigned NULL. In that case the result of evaluating X + 1 is NULL, and so SET Y = X + 1 assigns NULL
Overloading: Similar to packaged subprograms, methods of the same type can be overloaded. That is, you can use similar name for various methods if their formal parameters diff
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