Use of DECODE and NULL value in a WHERE clause

Question

hi all,
I came into an issue trying to use the DECODE function in a simple where clause.
this is my test case
CREATE TABLE tab_test (lev NUMBER, code VARCHAR2(10), val VARCHAR2(10));
INSERT INTO tab_test VALUES (1, NULL, 'val11');
INSERT INTO tab_test VALUES (1, NULL, 'val12');
INSERT INTO tab_test VALUES (1, '13', 'val13');
INSERT INTO tab_test VALUES (2, '21', 'val21');
INSERT INTO tab_test VALUES (1, '22', 'val22');
INSERT INTO tab_test VALUES (1, '23', 'val23');
and this is the query
SELECT * FROM tab_test WHERE code = DECODE(:lev,1,NULL,:cod)
as you can see running this query, setting :lev to 1 will return an empty record set, instead of the expected first two rows (as it will be, running "select * from tab_test where code is null").
is there a way to overcome this issue? thanks for help

Answer 1

hi Frank,
I can confirm that the queries do work when run on TOAD, but do not when they are put in the WHERE clause of my data block. I guess the problem relies on some data block setting; I should investigate on Forms forum.
Anyway, here is my test case, including data and some examples. You can realize that it works good
CREATE TABLE TAB_TEST
LEV NUMBER,
CODE VARCHAR2(10 BYTE),
VAL VARCHAR2(10 BYTE)
Insert into tab_test
(LEV, CODE, VAL)
Values
(3, 'val21', 'val3_211');
Insert into tab_test
(LEV, CODE, VAL)
Values
(2, 'val21', 'val3_212');
Insert into tab_test
(LEV, VAL)
Values
(1, 'val11');
Insert into tab_test
(LEV, VAL)
Values
(1, 'val12');
Insert into tab_test
(LEV, VAL)
Values
(1, 'val13');
Insert into tab_test
(LEV, CODE, VAL)
Values
(2, 'val11', 'val21');
Insert into tab_test
(LEV, CODE, VAL)
Values
(2, 'val12', 'val22');
Insert into tab_test
(LEV, CODE, VAL)
Values
(2, 'val13', 'val23');
COMMIT;
SELECT * FROM TAB_TEST
CONNECT
BY PRIOR val = code
START WITH (CASE
WHEN :LIV = 1 AND code IS NULL THEN 'OK'
WHEN :LIV != 1 AND code = :COD THEN 'OK'
END = 'OK')
               AND VAL = :V
:LIV = 1
:COD = [any]
:V = 'val11'
LEV     CODE     VAL
1          val11
2     val11     val21
3     val21     val3_211
3     val21     val3_212
:LIV = 1
:COD = [any]
:V = 'val12'
LEV     CODE     VAL
1          val12
2     val12     val22
:LIV = 2
:COD = 'val11'
:V = 'val21'
LEV     CODE     VAL
2     val11     val21
3     val21     val3_211
2     val21     val3_212