ALTER TABLE measurement_y2008m02 ADD CONSTRAINT y2008m02 CHECK ( logdate >= DATE '2008-02-01' AND logdate < DATE '2008-03-01' );
If logdate is indexed, then this constraint can be manually validated very quickly using a SELECT that will take advantage of the index
SELECT 1 FROM measurement_y2008m02 WHERE logdate < DATE '2008-02-01' OR logdate >= DATE '2008-03-01' LIMIT 1
If the constraint is valid the query will return quickly with no rows, if any rows violate the constraint it will also return very quickly but return with a single row with column value: 1.
I guess that validating constraints doesn't invoke the query planner, or otherwise the conversion is too complex for the query planner. The conversion being:
from: NOT (logdate >= DATE '2008-02-01' AND logdate < DATE '2008-03-01')
to: logdate < DATE '2008-02-01' OR logdate >= DATE '2008-03-01'
On Fri, Nov 15, 2024 at 4:38 PM Philip Couling <couling@gmail.com> wrote: > > Is there a solid reason why adding a check constraint does not use existing indexes for validation. >
can you give an sql example (except not-null) where indexes can be used for check constraint validation? i am not sure I understand it correctly.
