Re: creating CHECK constraints as NOT VALID

Excerpts from Jaime Casanova's message of mié jun 15 02:09:15 -0400 2011:

> psql \h says (among other things) for ALTER TABLE
> """
>    ADD table_constraint
>    ADD table_constraint_using_index
>    ADD table_constraint [ NOT VALID ]
> """
> 
> ADD table_constraint appears twice and isn't true that all
> table_constraint accept the NOT VALID syntax... maybe we can accpet
> the syntax and send an unimplemented feature message for the other
> table_constraints?
> 
> attached, is a script with the examples i have tried:
> 
> EXAMPLE 1:
> constraint_exclusion when using NOT VALID check constraints... and it
> works well, except when the constraint has been validated, it keeps
> ignoring it (which means i won't benefit from constraint_exclusion)
> until i execute ANALYZE on the table or close connection

Here's an updated patch fixing all of the above.  I stole your first
test case and added it to regression, after some editorialization.

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Álvaro Herrera <alvherre@commandprompt.com>
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