I am not asking difference between them, my question is when we need to use “Union All” ?
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I am not asking difference between them, my question is when we need to use “Union All” ?
You would use UNION ALL when you really do need the multiple ‘copies’ of rows that would otherwise be removed when using UNION. It can also be faster on the query end, since the DB engine does not need to determine what are duplicates between the result sets.