Determine Oracle null == null

Question

I wish to search a database table on a nullable column. Sometimes the value I\'m search for is itself NULL. Since Null is equal to nothing, even NULL, saying

Answer 1

@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...

Answer 2

Use NVL to replace null with some dummy value on both sides, as in:

WHERE NVL(MYCOLUMN,0) = NVL(SEARCHVALUE,0)

Answer 3

This is a situation we find ourselves in a lot with our Oracle functions that drive reports. We want to allow users to enter a value to restrict results or leave it blank to return all records. This is what I have used and it has worked well for us.

WHERE rte_pending.ltr_rte_id = prte_id
  OR ((rte_pending.ltr_rte_id IS NULL OR rte_pending.ltr_rte_id IS NOT NULL)
      AND prte_id IS NULL)

Answer 4

I don't know if it's simpler, but I've occasionally used

WHERE ISNULL(MyColumn, -1) = ISNULL(SearchValue, -1)

Replacing "-1" with some value that is valid for the column type but also not likely to be actually found in the data.

NOTE: I use MS SQL, not Oracle, so not sure if "ISNULL" is valid.

Answer 5

I would think that what you have is OK. You could maybe use:

where NVL(MYCOLUMN, '') = NVL(SEARCHVALUE, '')