SQL Case Statement Syntax?

What is the complete and correct syntax for the SQL Case statement?


Solution :

The complete syntax depends on the database engine you're working with:
For SQL Server:
CASE case-expression
    WHEN when-expression-1 THEN value-1
  [ WHEN when-expression-n THEN value-n ... ]
  [ ELSE else-value ]
END
or:
CASE
    WHEN boolean-when-expression-1 THEN value-1
  [ WHEN boolean-when-expression-n THEN value-n ... ]
  [ ELSE else-value ]
END
expressions, etc:
case-expression    - something that produces a value
when-expression-x  - something that is compared against the case-expression
value-1            - the result of the CASE statement if:
                         the when-expression == case-expression
                      OR the boolean-when-expression == TRUE
boolean-when-exp.. - something that produces a TRUE/FALSE answer
Also note that the ordering of the WHEN statements is important. You can easily write multiple WHEN clauses that overlap, and the first one that matches is used.
Note: If no ELSE clause is specified, and no matching WHEN-condition is found, the value of the CASE expression will be NULL.

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