You can't use a case statement expression to modify the query in that way. As I understand it you are trying to say - "see if cc_mtrl BETWEEN 1 and 550 is true IF (but only if) cc_check1 = 0, OTHERWISE see if cc_mtrl NOT BETWEEN 1 and 550 is true"

You need to restructure the where clause something like this (untested):

WHERE (cc_check = 0 and cc_mtrl BETWEEN 1 and 550)
   OR (cc_check != 0 and cc_mtrl NOT BETWEEN 1 and 550)

(corrected per Mark's comment below)

From section 3.10.1 IF and CASE Expressions  in "the book" ...

<searched_case_expression> ::= CASE
WHEN <boolean_expression> THEN <expression>
{ WHEN <boolean_expression> THEN <expression> }
[ ELSE <expression> ]
END

Caveat Emptor: I have not tested this code...

The CASE expression computes and returns a value, so compute that value and compare it with something.

WHERE CASE WHEN <boolean_expression1> THEN 1
           WHEN <boolean_expression2> THEN 1
           WHEN <boolean_expression3> THEN 1
           WHEN <boolean_expression4> THEN 1
           ELSE 0
      END = 1

I'm not sure what you're trying to accomplish, but maybe this works...

WHERE CASE WHEN cc_check1 = 0 AND cc_mtrl BETWEEN 1 and 550 THEN 1
           WHEN cc_mtrl NOT BETWEEN 1 and 550               THEN 1
           ELSE 0
      END = 1

Based on your last comment, I assume the following:

• When the string values "invalue", "invalue2" and "invalue3" are not empty, the dependend condition should be applied.
• Within each condition, the according flag ("cc_check", "cc_check2" and "cc_check3") decides whether the values "cc_mtrl" should lie within or outside a certain range.
• What I do not know is whether the 3 string values exclude each other or not (i.e. can "invalue" and "invalue2" both be non-empty?). - Here I assume they do not exclude each other, and the 3 conditions will be ORed.
• What I also do not know is what your desired result is: just a filter that includes the rows that fulfill the conditions, or a particular count (like in Justin's last comment)? - Here is assume the former.
• UPDATE based on Rolle's last comment: In case all three string values are NULL or empty, do include all rows.

Then the following would do:

 
...
WHERE
      (    len(invalue) > 0
       AND (   (cc_check = 0  AND cc_mtrl     BETWEEN 1 AND 550)
            OR (cc_check != 0 AND cc_mtrl NOT BETWEEN 1 and 550)))
   OR
      (    len(invalue2) > 0
       AND (   (cc_check2 = 0  AND cc_mtrl     BETWEEN 65 AND 80)
            OR (cc_check2 != 0 AND cc_mtrl NOT BETWEEN 65 and 80)))
   OR
      (    len(invalue3) > 0
       AND (   (cc_check3 = 0  AND cc_mtrl     BETWEEN 110 AND 180)
            OR (cc_check3 != 0 AND cc_mtrl NOT BETWEEN 110 AND 180)))
   OR
      (    len(isnull(invalue, '') = 0
       AND len(isnull(invalue2, '') = 0
       AND len(isnull(invalue3, '') = 0)

Note, if you have further contitions, you may need to add another set of brackets around the above conditions. Also note that some of the brackets could be omitted (AND has always higher precedence than OR), in case you and your collegues are aware of that...

And a further note: When one of the string values is null, len() will also return NULL, turning the whole condition into UNKNOWN - but that's just fine here, as "UNKNOWN OR x" will evaluate to "x", i.e. the whole condition of that string value will be omitted. Of course, if all three string values would be empty or null, the WHERE clause will not return any rows. UPDATE: Via the fourth condition, in case all three string values are empty/null, all rows are returned.