Name
CASE — Conditional expression evaluation
Syntax
Example Usage
CASE WHEN col IS NULL THEN 'null' WHEN NOT col THEN 'false' -- convert to logic value WHEN NOT NOT col THEN 'true' -- convert to logic value ELSE 'unknown' END
Description
The CASE
expression is similar to the C switch
statement, or a series of
if-then statements. The expression consists of an optional test
expression followed by one or more WHEN...THEN
clauses. The statement is
finished with an optional ELSE
clause and a required END
keyword.
Each WHEN...THEN
clause is evaluated in order. The
first WHEN
expression that is
found to be equivalent to the test expression will cause the
whole CASE
expression to take
the value of the corresponding return expression. If no
equivalent WHEN
expression is
found, the default expression value is used. If no ELSE
clause is provided, the
default expression is assumed to be NULL.
If no test expression is given,
the first WHEN
expression
that evaluates to true will be used.
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