The CASE statement - Amazon Timestream
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The CASE statement

The CASE statement searches each value expression from left to right until it finds one that equals expression. If it finds a match, the result for the matching value is returned. If no match is found, the result from the ELSE clause is returned if it exists; otherwise null is returned. The syntax is as follows:

CASE expression
    WHEN value THEN result
    [ WHEN ... ]
    [ ELSE result ]
END

Timestream also supports the following syntax for CASE statements. In this syntax, the "searched" form evaluates each boolean condition from left to right until one is true and returns the matching result. If no conditions are true, the result from the ELSE clause is returned if it exists; otherwise null is returned. See below for the alternate syntax: 

CASE
    WHEN condition THEN result
    [ WHEN ... ]
    [ ELSE result ]
END