subselect in CHECK constraint?

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When I try to do this:

CREATE TABLE test (
    a Integer,
    b Integer,
    CHECK ((SELECT SUM(t.a) FROM test t WHERE t.b = b) < 1000)
);

INSERT INTO test (a, b) VALUES (100, 2);

I get this error on the second query:

ERROR:  ExecEvalExpr: unknown expression type 108

I'm guessing this means I can't do subselects in CHECK statements.

Let me pose another question, if this is the case:

Say I have a table of warehouses. I then want to have another table keep
track of the products at the warehouse, such that the amount of product at
a warehouse does not exceed the capacity of the warehouse. Which probably
means I would need to have a CHECK statement with a select on each side of
the operator.

Any ideas? :o

I'd look at the source to see what this error means, except that I am on a
dialup.

Ian Turner
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