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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;
Using Operator VALUE: As you may expect, the operator VALUE returns the value of an object. The VALUE takes its argument a correlation variable. For illustration, to return a
UPDATE Statement The UPDATE statement transforms the values of the specified columns in one or more rows in the table or view. Syntax:
Ensuring Backward Compatibility The PL/SQL Version 2 permits some abnormal behavior which Version 8 disallows. Particularly, Version 2 permits you to (i) Make the forw
EXIT Statement You can use the EXIT statement to exit a loop. The EXIT statement has 2 forms: the conditional EXIT WHEN and the unconditional EXIT. With the either form, you
Example of WHEN or THEN Constraints A concrete example showing how SQL supports WHEN/THEN constraints CREATE TABLE SAL_HISTORY (EmpNo CHAR (6), Salary INTEGER NOT NULL,
Positional and Named Notation You can write the actual parameters when calling a subprogram, using either positional or named notation. That is, you can point to the relationsh
Project Description: I want to write some SQL statements. The things I need are between pages 5-7. The only problem is that i want it till tomorrow. Skills required is SQL
I have a Pascal Source file that needs to be compiled into a Service. In addition, there are various functions (Pascal Procedures I guess) that need to be created to Read and Write
a. Create a table odetails_new. It has all the attributes of odetails and an additional column called cost, whose values are the product of the quantity and price of the part bein
GOTO Statement The GOTO statement branches categorically to a block label or statement label. The label should be exclusive within its scope and should precede a PL/SQL bloc
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