How do you optimize SQL queries ?
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Answer Posted / hutashan
Avoid implicit datatype conversion
Avoid using function on an indexed column
Avoid comparing column value with NULL
Outer Join
Use OR carefully
Always use NOT EXISTS instead of NOT IN
Use UNION ALL whenever possible (no implicit sorts)
UNION will sort the result set for each SELECT before
combining the final result set
Remove DISTINCT keyword from SELECT if UNION is used
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