Monday, July 23, 2012

UNION VS UNION ALL

UNION VS UNION ALL

UNION

The UNION command is employed to pick connected info from 2 tables, very similar to the be a part of command. However, when using the UNION command all selected columns have to be compelled to be of constant knowledge kind. With UNION, solely distinct values are selected.


UNION ALL

The UNION ALL command is equal to the UNION command, except that UNION ALL selects all values.

The distinction between Union and Union all is that Union all won't eliminate duplicate rows, instead it simply pulls all rows from all tables fitting your question specifics and combines them into a table.

A UNION statement effectively will a pick DISTINCT on the results set. If you recognize that each one the records came back are distinctive from your union, use UNION ALL instead, it offers faster results.

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