If you are satisfied with only a one-directional constraint (apply the
check just when the constrained table is modified), you can have it today.
Just put the SELECT into a function that's called by the CHECK
expression.
Tom, you've just provided the solution to something I've been thinking about a lot. I really have to start thinking in terms of functions. Are there any restrictions on the function used in the CHECK, i.e., it must be STRICT or IMMUTABLE? I took a quick look at the developer docs (thinking they'd be for 7.4RC1. I was happily suprised to see they're already labeled 7.5 dev!)
Michael grzm myrealbox com
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