What Is a Subquery?
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What Is a Subquery?
by Micheal Sun Jan 17, 2010 3:16 am
A subquery is a SELECT statement used as part of the selection criteria of the main SELECT
statement. The subquery specified in the WHERE clause will be evaluated repeated on each row
of the selection base table. The output of the subquery will be used in the final evaluation of the
criteria. Usually, subqueries are used in the following boolean operations:
"expression IN (subquery)"
"expression NOT IN (subquery)"
"EXISTS (subquery)"
"NOT EXISTS (subquery)"
statement. The subquery specified in the WHERE clause will be evaluated repeated on each row
of the selection base table. The output of the subquery will be used in the final evaluation of the
criteria. Usually, subqueries are used in the following boolean operations:
"expression IN (subquery)"
"expression NOT IN (subquery)"
"EXISTS (subquery)"
"NOT EXISTS (subquery)"
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» Accessing tables of other users in SQL
» Grouping commands in SQL
» Operations on Result Sets in SQL
» Subqueries in SQL
» Joining Relations in SQL
» Delete comand in SQL
» Update command in SQL
» Insert command in SQL