WHERE子句中的动态SQL

Question

SELECT A.COL1, A.COL2, A.COL3, A.COL4
FROM TABLE A, TABLE B
WHERE B.COL1 = A.COL1
AND B.COL2 = A.COL2
AND B.COL3 - A.COL3
AND B.COL4 = A.COL4

Now I want to tune the SQL query, that whenever any of the Columns in Table B has field value 'ALL' the where clause will not come into picture.

ie When it has a distinct value it will match with both the tables, when the field value is 'ALL' then to exclude from the where clause.

Alternatively,

I Need B.COL1= A.COL1 (When B.COL1 <> 'ALL')
Else NO WHERE clause with B.Col1 = A.Col1 (When B.COL1 = 'ALL')

Answer 1

Use OR wisely:

SELECT A.COL1, A.COL2, A.COL3, A.COL4
FROM TABLE A, TABLE B
WHERE (B.COL1 = A.COL1 OR B.COL1='ALL')
AND (B.COL2 = A.COL2 OR B.COL2='ALL')
...

I would also suggest learning JOIN syntax.

Answer 2

Hi,
You can use case statement to have a condition in where clause,

    SELECT A.COL1, A.COL2, A.COL3, A.COL4
FROM TABLE A, TABLE B
WHERE B.COL1 = 
              CASE 
              WHEN B.COL1 <> 'ALL' THEN A.COL1
              ELSE NULL
              END
      AND B.COL2 = A.COL2
      AND B.COL3 - A.COL3
      AND B.COL4 = A.COL4

Answer 3

You can achieve this with just IN:

SELECT A.COL1, A.COL2, A.COL3, A.COL4
FROM TABLE A, TABLE B
WHERE B.COL1 IN (A.COL1, 'ALL')
AND B.COL2 IN (A.COL2, 'ALL')
AND B.COL3 IN (A.COL3, 'ALL')
AND B.COL4 IN (A.COL4, 'ALL')

What is actually going on may be more clear with a more verbose version using AND/OR , but the logic is exactly the same

SELECT A.COL1, A.COL2, A.COL3, A.COL4
FROM TABLE A, TABLE B
WHERE (B.COL1 = A.COL1 OR B.COL1 = 'ALL')
AND (B.COL2 = A.COL2 OR B.COL2 = 'ALL')
AND (B.COL3 = A.COL3 OR B.COL3 = 'ALL')
AND (B.COL4 = A.COL4 OR B.COL4 = 'ALL')

Answer 4

Simple solution:

SELECT DISTINCT A.COL1, A.COL2, A.COL3, A.COL4
FROM TABLE A
INNER JOIN TABLE B ON 
(B.COL1 = A.COL1 AND B.COL2 = A.COL2 AND B.COL3 = A.COL3 AND B.COL4 = A.COL4)
OR
('ALL' IN (B.COL1, B.COL2, B.COL3, B.COL4))

but, if you work with large tables that complex filtering could slow down very much the execution, so I suggest to use a different syntax for complex JOINs

SELECT DISTINCT * 
FROM (
    SELECT A.COL1, A.COL2, A.COL3, A.COL4
    FROM A 
    INNER JOIN B 
    ON (B.COL1 = A.COL1 AND B.COL2 = A.COL2 AND B.COL3 = A.COL3 AND B.COL4 = A.COL4)
) J1

UNION -- ALL ?

SELECT DISTINCT * 
FROM (
    SELECT A.COL1, A.COL2, A.COL3, A.COL4
    FROM A 
    INNER JOIN B ON ('ALL' IN (B.COL1, B.COL2, B.COL3, B.COL4))
) J2 

This one should be much faster than previous one.

Also, I wonder about row duplicates.. with that syntax each row of table A will be added to result as many times as many rows in table B contains 'ALL'

I have added the DISTINCT clause to the SELECT to avoid duplicates (same problem affects UNION operator), so if you need duplicates, remove DISTINCT and use UNION ALL instead of UNION