Difference between revisions 774123026 and 797311035 on enwiki

{{Refimprove|date=September 2014}}
A <code>WHERE</code> clause in [[SQL]] specifies that a SQL [[Data Manipulation Language|Data Manipulation Language (DML)]] statement should only affect rows that meet specified criteria. The criteria are expressed in the form of predicates. <code>WHERE</code> clauses are not mandatory clauses of SQL DML statements, but can be used to limit the number of rows affected by a SQL DML statement or returned by a query. In brief SQL WHERE clause is used t(contracted; show full)
* Multiple Wildcards 	
** Find any string that contains, anywhere, the letter 'S'<source lang="sql">
SELECT ename FROM emp WHERE ename LIKE '%S%';</source>
* Single Character Wildcard 	
** Find any string that contains the letter 'A' followed by any single character followed by the letter 'E'<source lang="sql">
SELECT ename FROM emp WHERE ename LIKE '%A_E%';</source>
* Character Classes<ref>''[http
s://technet.microsoft.com/en-us/library/ms179859.aspx Microsoft Technet]''Retrieved 21 November 2013.</ref>
** Find any string that starts with a letter or number or the symbol '_'<source lang="sql">
SELECT ename FROM emp WHERE ename LIKE '[a-zA-Z0-9_]%';</source>
SQL programmers need to be aware that the LIKE predicate typically performs a search without the normal performance benefit of indexes. Using '=', '<>', etc.. instead will increase performance.  Users of the LIKE predicate should be aware that case sensitivity (e.g., 'S' versus 's') may be different based upon database product or configuration.

== References ==
<references />

== External links ==
* [http://www.psoug.org/reference/conditions.html PSOUG Home Puget Sound Oracle Users Group] gives several examples of SELECT statements with WHERE clauses.

{{SQL}}

[[Category:SQL keywords]]