Sandro == Sandro Santilli s...@keybit.net writes:
Sandro PostGIS installs standard constraints of this kind:
Sandro CHECK (geometrytype(g) = 'POINT'::text OR g IS NULL)
If geometrytype() is strict, the IS NULL condition is superfluous.
CHECK(x) _passes_ when x is null, rather than rejecting the row.
Sandro But it is _NOT_ used if the NOT NULL condition is removed:
Sandro WHERE geometrytype(g) = 'LINESTRING'
Sandro As the geometrytype is defined as STRICT and IMMUTABLE,
Sandro there's no way for geometrytype(g) = 'LINESTRING' to hold true,
Sandro so why is the IS NOT NULL condition also needed by the
Sandro planner ?
Sandro Andres Freund on IRC suggested that
Sandro predicate_refuted_by_simple_clause() looks like trying to
Sandro handle such cases, but if that's the case it seems to fail
It looks like it searches only one level deep into the clause, so it
knows that if OP or FUNC is strict that (g OP const) or (FUNC(g)) will
refute (g IS NULL), but not that (FUNC(g) OP const) will do so, because
the reference to g is nested too deep.
In this case the obvious thing to do is remove the redundant clause.
Whether it would be worth teaching the predicate prover to recurse in
such cases would be a performance tradeoff - likely a poor one, since it
would have to recurse into arbitrarily complex expressions.
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