Determine Oracle null == null
@Andy Lester asserts that the original form of the query is more efficient than using NVL. I decided to test that assertion:
SQL> DECLARE
2 CURSOR B IS
3 SELECT batch_id, equipment_id
4 FROM batch;
5 v_t1 NUMBER;
6 v_t2 NUMBER;
7 v_c1 NUMBER;
8 v_c2 NUMBER;
9 v_b INTEGER;
10 BEGIN
11 -- Form 1 of the where clause
12 v_t1 := dbms_utility.get_time;
13 v_c1 := dbms_utility.get_cpu_time;
14 FOR R IN B LOOP
15 SELECT COUNT(*)
16 INTO v_b
17 FROM batch
18 WHERE equipment_id = R.equipment_id OR (equipment_id IS NULL AND R.equipment_id IS NULL);
19 END LOOP;
20 v_t2 := dbms_utility.get_time;
21 v_c2 := dbms_utility.get_cpu_time;
22 dbms_output.put_line('For clause: WHERE equipment_id = R.equipment_id OR (equipment_id IS NULL AND R.equipment_id IS NULL)');
23 dbms_output.put_line('CPU seconds used: '||(v_c2 - v_c1)/100);
24 dbms_output.put_line('Elapsed time: '||(v_t2 - v_t1)/100);
25
26 -- Form 2 of the where clause
27 v_t1 := dbms_utility.get_time;
28 v_c1 := dbms_utility.get_cpu_time;
29 FOR R IN B LOOP
30 SELECT COUNT(*)
31 INTO v_b
32 FROM batch
33 WHERE NVL(equipment_id,'xxxx') = NVL(R.equipment_id,'xxxx');
34 END LOOP;
35 v_t2 := dbms_utility.get_time;
36 v_c2 := dbms_utility.get_cpu_time;
37 dbms_output.put_line('For clause: WHERE NVL(equipment_id,''xxxx'') = NVL(R.equipment_id,''xxxx'')');
38 dbms_output.put_line('CPU seconds used: '||(v_c2 - v_c1)/100);
39 dbms_output.put_line('Elapsed time: '||(v_t2 - v_t1)/100);
40 END;
41 /
For clause: WHERE equipment_id = R.equipment_id OR (equipment_id IS NULL AND R.equipment_id IS NULL)
CPU seconds used: 84.69
Elapsed time: 84.8
For clause: WHERE NVL(equipment_id,'xxxx') = NVL(R.equipment_id,'xxxx')
CPU seconds used: 124
Elapsed time: 124.01
PL/SQL procedure successfully completed
SQL> select count(*) from batch;
COUNT(*)
----------
20903
SQL>
I was kind of surprised to find out just how correct Andy is. It costs nearly 50% more to do the NVL solution. So, even though one piece of code might not look as tidy or elegant as another, it could be significantly more efficient. I ran this procedure multiple times, and the results were nearly the same each time. Kudos to Andy...
You can do the IsNull or NVL stuff, but it's just going to make the engine do more work. You'll be calling functions to do column conversions which then have to have the results compared.
Use what you have
where ((MYCOLUMN=SEARCHVALUE) OR (MYCOLUMN is NULL and SEARCHVALUE is NULL))