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."
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