SQL CASE Statement

Answer 1

try
SELECT CASE LEN(@gcode)
WHEN IN(x, y, z) THEN a
etc.

or you may need
SELECT CASE LEN(@gcode)
WHEN x THEN a
WHEN y THEN a
etc.

Here's the reference.

Answer 2

try this:

Select @Type = 
(select case 
WHEN len(@code) IN (12,14,17) THEN 1
WHEN len(@code) IN (13,15,18) THEN 2
WHEN len(@code) IN (8,10) THEN 3
ELSE  0
END)

Answer 3

This should do it:

CREATE FUNCTION getItemType(@code VARCHAR(18))
RETURNS INT
AS
BEGIN
    RETURN CASE 
     WHEN LEN(@code) IN (12,14,17) THEN 1
     WHEN LEN(@code) IN (13,15,18) THEN 2
     WHEN LEN(@code) IN (8,100)    THEN 3
     ELSE  0
    END
END