Hi,

The CASE expression by itself looks okay.  I'll bet the problem is how you're using the CASE expression.   Show enough of the context so anybody can re-produce the problem.

If you ever have a question about a SQL feature (such as CASE expressions), then you should post in in the SQL and PL/SQL Forum:

By the way, the CASE expression can be simplified a little

WHEN CLIENT_TYPE = 'ROLAND' THEN 'ROLAND' 
WHEN CLIENT_TYPE = 'LTDS' THEN 'LTDS'
WHEN CLIENT_TYPE = 'ALFIE' THEN 'ALFIE' 
WHEN CLIENT_TYPE = 'CSS_STI' THEN 'CSS_STI'
WHEN CLIENT_TYPE = 'AUTOFIXEMP' THEN 'AUTOFIXEMP' 
WHEN CLIENT_TYPE = 'RABIT' THEN 'RABIT'
WHEN CLIENT_TYPE = 'MPF_TEST_TOOL' THEN 'WOOSH' 
WHEN CLIENT_TYPE = 'BACK_OFFICE' THEN 'WOOSH'
WHEN CLIENT_TYPE = 'FRONT_OFFICE' THEN 'WOOSH' 

can be re-written as

WHEN CLIENT_TYPE IN ( 'ROLAND'
                    , 'LTDS'
                    , 'ALFIE'
                    , 'CSS_STI'
                    , 'AUTOFIXEMP'
                    , 'RABIT'
                    )       THEN  CLIENT_TYPE
WHEN CLIENT_TYPE IN ( 'MPF_TEST_TOOL'
                    , 'BACK_OFFICE'
                    , 'FRONT_OFFICE'
                    )       THEN 'WOOSH' 

Both get the same results, equally fast, but I find the latter way much easier to write, read, debug and maintain.