Operations requiring sorts

Operations that Require Temporary Segments
The following statements sometimes require the use of a temporary segment:

CREATE INDEX

SELECT ... ORDER BY

SELECT DISTINCT ...

SELECT ... GROUP BY

SELECT . . . UNION

SELECT ... INTERSECT

SELECT ... MINUS

Some unindexed joins and correlated subqueries can require use of a temporary segment. For example, if a query contains a DISTINCT clause, a GROUP BY, and an ORDER BY, Oracle can require as many as two temporary segments.

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