What is the main difference between a UNION statement and a
UNION ALL statement?
1. A UNION statement eliminates duplicate rows; a UNION
ALL statement includes duplicate rows.
2. A UNION statement can be used to combine any number of
queries; a UNION ALL statement can be used to combine a
maximum of two queries.
3. A UNION statement can only combine queries that have
parallel fields in the SELECT list; a UNION ALL statement
can combine queries with differing SELECT list structures.
4. A UNION statement cannot be used with aggregate
functions; a UNION ALL statement can be used with aggregate
functions.
5. There is no difference between the two statements; they
are interchangeable.
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Answer Posted / menan
A UNION statement eliminates duplicate rows; a UNION
ALL statement includes duplicate rows.
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