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.
Note: In a CASE statement, AND has precedence over OR.
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 Score-par
WHEN -5 THEN 'Birdie on Par 6'
WHEN -4 THEN 'Must be Tiger'
WHEN -3 THEN 'Three under par'
WHEN -2 THEN 'Two under par'
WHEN -1 THEN 'Birdie'
WHEN 0 THEN 'Par'
WHEN 1 THEN 'Bogey'
WHEN 2 THEN 'Double Bogey'
ELSE 'Triple Bogey or Worse'
END
In this example, the WHEN statements must reflect a strict equality. For example, a WHEN condition of WHEN < 0 THEN 'Under Par' is illegal because comparison operators are not allowed.
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.
Note: In a CASE statement, AND has precedence over OR.
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 score-par < 0 THEN 'Under Par'
WHEN score-par = 0 THEN 'Par'
WHEN score-par = 1 THEN 'Bogie'
WHEN score-par = 2 THEN 'Double Bogey'
ELSE 'Triple Bogey or Worse'
END
Unlike the Switch form of the CASE statement, the WHEN statements in the If form allow comparison operators. For example, a WHEN
condition of WHEN < 0 THEN 'Under Par' is legal.
