Use of CASE in Select

Question

Environment: Oracle 10gR1, Application Express 3.1.2, Windows XP
I am trying to do a conditional select within an Application express SQL report. I've tried the following code and gotten the indicated errors:
1. First try
SELECT find_id, fdno FROM find
WHERE site_abbrv_cd = :P43_SITE
AND season = :P43_SEASON
AND dig_ctgy_cd (
CASE
WHEN :P43_INFIX IN ('T','P','R') THEN
= :P43_INFIX
ELSE IS NULL
END)
ORDER BY display_seq_nbr
ORA-00936: missing expression
2. Second try:
SELECT find_id, fdno FROM find
WHERE site_abbrv_cd = :P43_SITE
AND season = :P43_SEASON
AND (
CASE
WHEN :P43_INFIX IN ('T','P','R') THEN
dig_ctgy_cd = :P43_INFIX
ELSE dig_ctgy_cd IS NULL
END)
ORDER BY display_seq_nbr
ORA-00905: missing keyword
Any suggestions for re-casting the query so that the "is null" condition can be tested when the Infix code is not 'T', or 'P' or 'R'?
thanks for any help
George

Answer 1

Hi, George,
Remember what a CASE expression does: it takes the place of a single value in one of the SQL data types.
For example, if you can say:
AND     dig_ctgy_cd = :p43_infix(where :p43_infix is a VARCHAR2, or a NUMBER, or any other SQL type) then you can say
AND     dig_ctgy_cd = CASE ... ENDThe is no BOOLEAN data type in SQL, so CASE can't return a BOOLEAN value. You could have a CASE expression that returned a string, such as '= :p43_infix', but you would have to use dynamic SQL to that this compiled as a condition, rather than a string literal.
Explain what you're trying to do, and someone will help you find a way to do it.
Perhaps you want something like this:
AND     dig_ctgy_cd || 'X'    = CASE
                               WHEN  :p43_infix IN ('T', 'P', 'R')
                        THEN  :p43_infix
                       END || 'X'Post a little sample data (CREATE TABLE and INSERT statements), a couple of values of :p43_infix, and the results you want from the same sample data for each value of :p43_infix.
Edited by: Frank Kulash on Jul 19, 2011 4:04 PM