OQL Case Expression

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1 Description

The CASE expression is a conditional expression, similar to if/else statements in other programming languages. Each condition is an expression that returns a Boolean result. If the condition’s result is true, the value of the CASE expression is the result that follows the condition, and the remainder of the CASE expression is not processed. If the condition’s result is not true, any subsequent WHEN clauses are examined in the same manner. If no WHEN condition yields true, the value of the CASE expression is the result of the ELSE clause. If the ELSE clause is omitted and no condition is true, the result is null.

2 Usage

The CASE expression can be used in two ways – simple:

	CASE input_expression
	WHEN when_expression THEN result_expression [ ...n ]
	ELSE else_result_expression
	END

or extended:

	CASE
	WHEN boolean_expression THEN result_expression [ ...n ] 
	ELSE else_result_expression
	END

3 Syntax

3.1 input_expression

input_expression will be compared to when_expression. If input_expression matches when_expression, the result of the whole CASE expression will be result_expression given after THEN.

3.2 when_expression

when_expression will be compared to input_expression. When input_expression matches this when_expression, the result of the whole CASE expression will be result_expression given after THEN.

3.3 boolean_expression

boolean_expression must result in a Boolean value. When this expression returns true, the result of the whole CASE expression will be result_expression given after THEN.

3.4 result_expression

result_expression is the possible result of the whole CASE expression.

3.5 else_result_expression

else_result_expression is the result of the whole CASE expression, when no result_expression is possible.