Favourite performance tuning tricks [closed]

Answer 1

Convert NOT IN queries to LEFT OUTER JOINS if possible. For example if you want to find all rows in Table1 that are unused by a foreign key in Table2 you could do this:

SELECT *
FROM Table1
WHERE Table1.ID NOT IN (
    SELECT Table1ID
    FROM Table2)

But you get much better performance with this:

SELECT Table1.*
FROM Table1
LEFT OUTER JOIN Table2 ON Table1.ID = Table2.Table1ID
WHERE Table2.ID is null