<p>What is the <strong>complete</strong> and correct syntax for the SQL Case expression?</p>

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
```
```
Link:
CASE (Transact-SQL)
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
.