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Difference between Distinct and Unique March 9, 2007

Posted by Muhammad Habib in Oracle General.

Specify DISTINCT or UNIQUE if you want Oracle to return only one copy of each set of duplicate rows selected (these two keywords are synonymous). Duplicate rows are those with matching values for each expression in the select list.Restrictions on DISTINCT and UNIQUE Queries

  • When you specify DISTINCT or UNIQUE, the total number of bytes in all select list expressions is limited to the size of a data block minus some overhead. This size is specified by the initialization parameter DB_BLOCK_SIZE.
  • You cannot specify DISTINCT if the select_list contains LOB columns.


1. Idetrorce - December 16, 2007

very interesting, but I don’t agree with you

2. music - January 6, 2008

very interesting.
i’m adding in RSS Reader

3. Mark Mestetskiy - April 9, 2009

I beleive there is another difference, may be not exactly related to Oracle. UNIQUE is Oracle proprietary term. DISTINCT is more standard used in ANSI SQL. While Disctinct will work with MySQL or other similar products, UNIQUE – won’t.

4. Habib Gohar - April 10, 2009

Thanks for your comments MARK

5. dbametrix - October 21, 2009


Exactly Habib and Mark both are right in way of explain in same topic.

Thanks and regards,

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