CASE (Entity SQL)

Artikkeli
09/15/2021

Evaluates a set of Boolean expressions to determine the result.

Syntax

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

Arguments

n Is a placeholder that indicates that multiple WHEN Boolean_expression THEN result_expression clauses can be used.

THEN result_expression Is the expression returned when Boolean_expression evaluates to true. result expression is any valid expression.

ELSE else_result_expression Is the expression returned if no comparison operation evaluates to true. If this argument is omitted and no comparison operation evaluates to true, CASE returns null. else_result_expression is any valid expression. The data types of else_result_expression and any result_expression must be the same or must be an implicit conversion.

WHEN Boolean_expression Is the Boolean expression evaluated when the searched CASE format is used. Boolean_expression is any valid Boolean expression.

Return Value

Returns the highest precedence type from the set of types in the result_expression and the optional else_result_expression.

Remarks

The Entity SQL case expression resembles the Transact-SQL case expression. You use the case expression to make a series of conditional tests to determine which expression will yield the appropriate result. This form of the case expression applies to a series of one or more Boolean expressions to determine the correct resulting expression.

The CASE function evaluates Boolean_expression for each WHEN clause in the order specified, and returns result_expression of the first Boolean_expression that evaluates to true. The remaining expressions are not evaluated. If no Boolean_expression evaluates to true, the Database Engine returns the else_result_expression if an ELSE clause is specified, or a null value if no ELSE clause is specified.

A CASE statement cannot return a multiset.

Example

The following Entity SQL query uses the CASE expression to evaluate a set of Boolean expressions in order to determine the result. The query is based on the AdventureWorks Sales Model. To compile and run this query, follow these steps:

Follow the procedure in How to: Execute a Query that Returns PrimitiveType Results.
Pass the following query as an argument to the ExecutePrimitiveTypeQuery method:

CASE WHEN AVG({@score1,@score2,@score3}) < @total THEN TRUE ELSE FALSE END

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