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CASE Expression

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With a case expression it is possible to specify a conditional value. Depending on the result of one or more conditional expressions the case expression can return different values.

A CASE expression can be in one of the following two forms:

Example:

 CASE WHEN col1 < 10  THEN 1
 WHEN col1 >= 10 THEN 2
 ELSE 3
 END
 

Example:

 CASE col1 WHEN 0 THEN NULL
 WHEN -1 THEN -999
 ELSE col1
 END

Rules:

• If one or more search-conditions are true, then the result of the CASE expression is the result of the first (left-most) WHEN clause which has a search-condition that is true.
• If none of the search-conditions are true, then the result of the CASE expression is the result of the explicit or implicit ELSE clause.
• If no ELSE clause is specified then ELSE NULL is implicit.
• At least one result in a CASE expression must express a value different from NULL.

See Result Data Types for a description of how the data type of the result of the CASE expression is determined.

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