11.2 Assignments and Statements

The assignment operator is:

 ":=" 

The assignment operator is not "=", but the if-test expression is.

 IF (a = b) 

We do not code:

 IF (a == b) 

You can assign literal values, or expressions that include operations and other variables . You can wrap expressions provided the statement does not break in the middle of a variable name .

 base_monthly_salary  := 10000; base_salary_increase := 1000; new_professor_salary := base_monthly_salary * 1.1; new_profrssor_salary := base_monthly_salary +                         base_salary_increase; 

You can declare a variable with an initialized value. You can initialize it with NULL. Do not assume any initial value of a variable that is declared with no initial setting. You can declare an initialized variable and constrain it to NOT NULL. The following PL/SQL declares several variables.

 DECLARE     total_credits      NUMBER(3,1);     total_credits_2    NUMBER(3,1) := NULL;     credit_hour        NUMBER(2,1) := 3.0;     no_credit CONSTANT NUMBER(2,1) := 0;     pass_fail_credit   NUMBER(2,1) NOT NULL := 0; BEGIN  PL/SQL code here.  END; 

TOTAL_CREDITS	This is a basic declaration of a NUMBER for three digits: two to the left of the decimal point, one place to the right.
TOTAL_CREDITS_2	Same as TOTAL_CREDITS except the variable is initialized to NULL.
CREDIT_HOUR	This variable has a default assignment. The value can change anytime within the code block.
NO_CREDIT	This is a constant. Constants are a form of self-documenting code. When you use a constant, you are documenting the fact that this variable is to have no other value.
PASS_FAIL_CREDIT	If you declare a variable as NOT NULL, then you must assign a default value in the same declaration.

You can code a NULL statement. For example, the following is a valid PL/SQL block and when executed, declares variables and exits.

 DECLARE     total_credits      NUMBER(3,1);     total_credits_2    NUMBER(3,1) := NULL;     credit_hour        NUMBER(2,1) := 3.0;     no_credit CONSTANT NUMBER(2,1) := 0;     pass_fail_credit   NUMBER(2,1) NOT NULL := 0; BEGIN     NULL; END; 

A common use of the NULL statement is within an exception handler where you want to catch the exception but intend no action. For example:

 EXCEPTION     WHEN DUP_VAL_ON_INDEX THEN NULL; END;