12 March 2012

Conditional Expressions ( Function )


Conditional Expressions


Expressions are building blocks for creating conditional expressions that convert a value from one form to another. Expressions include:

·         CASE (Switch)

·         CASE (If)

CASE (Switch)


This form of the CASE statement is also referred to as the CASE(Lookup) form. The value of expr1 is examined, then the WHEN expressions. If expr1 matches any WHEN expression, it assigns the value in the corresponding THEN expression.

If none of the WHEN expressions match, it assigns the default value specified in the ELSE expression. If no ELSE expression is specified, the system automatically adds an ELSE NULL.

If expr1 matches an expression in multiple WHEN clauses, only the expression following the first match is assigned.

Syntax

CASE expr1
     WHEN expr2 THEN expr3
     {WHEN expr... THEN expr...}
     ELSE expr
END 

Where:

CASE starts the CASE statement. Must be followed by an expression and one or more WHEN and THEN statements, an optional ELSE statement, and the END keyword.

WHEN specifies the condition to be satisfied.

THEN specifies the value to assign if the corresponding WHEN expression is satisfied.

ELSE specifies the value to assign if none of the WHEN conditions are satisfied. If omitted, ELSE NULL is assumed.

END ends the CASE statement.

Example

CASE "TableHeading"."Column Name" 
WHEN 'Col_Val1' THEN 'Val1' 
WHEN 'Col_Val2' THEN 'Val2' 
WHEN 'Col_Val3' THEN 'Val3' 
ELSE "TableHeading"."Column Name" 
END

In this example, the WHEN statements must reflect a strict equality. 

CASE (If)


This form of the CASE statement evaluates each WHEN condition and if satisfied, assigns the value in the corresponding THEN expression.

If none of the WHEN conditions are satisfied, it assigns the default value specified in the ELSE expression. If no ELSE expression is specified, the system automatically adds an ELSE NULL.


Syntax

CASE 
     WHEN request_condition1 THEN expr1
     {WHEN request_condition2 THEN expr2}
     {WHEN request_condition... THEN expr...}
     ELSE expr
END 

Where:

CASE starts the CASE statement. Must be followed by one or more WHEN and THEN statements, an optional ELSE statement, and the END keyword.

WHEN specifies the condition to be satisfied.

THEN specifies the value to assign if the corresponding WHEN expression is satisfied.

ELSE specifies the value to assign if none of the WHEN conditions are satisfied. If omitted, ELSE NULL is assumed.

END ends the CASE statement.

Example

CASE 
WHEN ("TableHeading"."ColumnName1"='Val_A' AND "TableHeading"."ColumnName"='Value1') THEN 'Val1' 
WHEN ("TableHeading"."ColumnName2"='Val_B' AND "TableHeading1"."ColumnName2"='Value2') THEN 'Val2' 
WHEN "TableHeading"."Column Name"='Value3' THEN 'Val3' 
ELSE "TableHeading"."Column Name" 
END

Note :
Unlike the case-switch form, the WHEN statements in the case-if form allow comparison operators in a CASE statement, AND has precedence over OR.