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List:       postgresql-general
Subject:    Re: [GENERAL] Documentation clairification?, CHECK constraints
From:       "Karl O. Pinc" <kop () meme ! com>
Date:       2004-03-31 18:27:47
Message-ID: 20040331122747.I1749 () mofo ! meme ! com
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On 2004.03.31 10:53 Tom Lane wrote:
> "Karl O. Pinc" <kop@meme.com> writes:
> > But SQL has 3 valued logic (strictly speaking, not boolean).  It
> > seems that the CHECK clases fail only when the expression result
> > is FALSE, and pass when the result is either TRUE or UNKNOWN.
> 
> Correct --- this is per spec.
> 
> > Yes?  Should this be clarified in the documentation?
> 
> Sure, send a documentation patch.

--- create_table.sgml   Wed Mar 31 12:57:02 2004
+++ create_table.sgml.new       Wed Mar 31 13:16:55 2004
@@ -383,11 +383,14 @@
       <para>
        The <literal>CHECK</> clause specifies an expression producing a
        Boolean result which new or updated rows must satisfy for an
-      insert or update operation to succeed.  A check constraint
-      specified as a column constraint should reference that column's
-      value only, while an expression appearing in a table constraint
-      may reference multiple columns.
+      insert or update operation to succeed.  Expressions evaluating
+      to TRUE or UNKNOWN succeed.  Should any row of an insert or
+      update operation produce a FALSE result an error exception is
+      raised and the insert or update does not alter the database.  A
+      check constraint specified as a column constraint should
+      reference that column's value only, while an expression
+      appearing in a table constraint may reference multiple columns.
       </para>
        <para>

Karl <kop@meme.com>
Free Software:  "You don't pay back, you pay forward."
                  -- Robert A. Heinlein

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