Faster way of doing multiple checks on one dataset - sql

Question

Is there a better way to rewrite the following:
SELECT DISTINCT Column1, 'Testing #1'
FROM MyTable
WHERE Column2 IS NOT NULL && Column3='Value'
UNION ALL
SELECT DISTINCT Column1, 'Testing #2'
FROM MyTable
WHERE Column3 IS NULL && Column2='Test Value'
UNION ALL
SELECT DISTINCT Column1, 'Testing #3'
FROM MyTable
Where ....
In have about 35 union all statements that all query the same table. I was wondering if there's an easier/faster way to do things.

Answer 1

Yes, you can rewrite it with case statements like this
SELECT Column1,
CASE WHEN Column2 IS NOT NULL AND Column3='Value' THEN 'Testing #1'
WHEN Column3 IS NULL AND Column2='Test Value' THEN 'Testing #2'
ELSE 'Testing #3' END as customcol
FROM MyTable
EDIT : Ok, i am making this edit because according to your comment, there are two issues we need to address. (I am leaving the original answer as it is in case it might help somebody.)
1) Result set should be filtered and there should be no else part.
This is actually achievable with this solution since else is optional and data can be filtered with a where clause at the end.
2) Being able to select the same row multiple times with different Testing # values if it matches the criteria.
This however is not achievable with my previous solution. So i thought of a different one. Hope it fits into your case. Here it is
S1 - Create a new table with Testing # values(Testing #1, Testing #2, Testing #3 etc.). Let's say this table is named Testing.
S2 - JOIN your main table (MyTable) with Testing table which contains Testing # values. So now you have every possible combination of real-data and testing values.
S3 - Filter the results you don't want to appear with a where clause.
S4 - Filter the real-data <-> testing combinations with an addition to where clause.
End query should look something like this :
SELECT M.Column1, T.TestingValue
FROM MyTable M
INNER JOIN Testing T ON 1=1
WHERE
(
(M.Column2 IS NOT NULL AND M.Column3='Value' AND T.TestingValue='Testing #1') OR
(M.Column3 IS NULL AND M.Column2='Test Value' AND T.TestingValue='Testing #2') OR
<conditions for other testing values>
)
AND
<other conditions>
I think this should work and produce the results you want. But since i don't have the data i am not able to run any benchmarks vs the union-based solution. So i don't have any scientific evidence to claim this is faster but it is an option. You can test both and use the better one.
It might be a little late but hope this solves your problem.

Answer 2

You can do this in one statement, but you want a different column for each test:
select column1,
(case when column2 is not null and column3 = 'Value' then 1 else 0
end) as Test1
(case when column3 is null and column3 = 'Test Value' then 1 else 0
end) as Test2,
. . .
from t;
Because you only want cases where things fail, you can put this in a subquery and test for any failure:
select *
from (select column1,
(case when column2 is not null and column3 = 'Value' then 1 else 0
end) as Test1
(case when column3 is null and column3 = 'Test Value' then 1 else 0
end) as Test2,
. . .
from t
) t
where test1 + test2 + . . . > 0