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[doc] complete description of EXISTS in rql/language.rst stable
authorNicolas Chauvat <nicolas.chauvat@logilab.fr>
Tue, 15 Mar 2011 10:38:02 +0100
branchstable
changeset 7081 6beb7f1e05fa
parent 7080 a828feedc164
child 7082 1b07eb7180a2
[doc] complete description of EXISTS in rql/language.rst
doc/book/en/annexes/rql/language.rst file | annotate | diff | comparison | revisions 
--- a/doc/book/en/annexes/rql/language.rst	Tue Mar 15 09:41:45 2011 +0100
+++ b/doc/book/en/annexes/rql/language.rst	Tue Mar 15 10:38:02 2011 +0100
@@ -153,7 +153,7 @@
 - Aggregate Functions: COUNT, MIN, MAX, AVG, SUM, GROUP_CONCAT
 
 Having
-``````
+```````
 
 The HAVING clause, as in SQL, has been originally introduced to restrict a query
 according to value returned by an aggregate function, e.g.::
@@ -214,7 +214,12 @@
 
 
 Exists
-``````
+```````
+
+You can use `EXISTS` when you want to know if some expression is true and do not
+need the complete set of elements that make it true. Testing for existence is
+much faster than fetching the complete set of results.
+
 ::
 
     Any X ORDERBY PN,N
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