On Mon, 9 Jun 2003, Forest Wilkinson wrote:
> I need to enumerate the constraints on any given column in a table, so
> I'm examining pg_constraint to get the relevant information. The
> conkey array contains a list of constrained columns, and although I am
> able to check conkey[1] for constraints on a single column, I would
> like to properly handle multi-column constraints.
>
> How do I determine the size of the conkey array? I haven't found any
> field that looks like it contains the number of values in conkey. Do
> I have to check each element of the array sequentially, until I get a
> NULL value from one of them? (Section 5.12 of the User's Guide seems
> to forbid this: "A limitation of the present array implementation is
> that individual elements of an array cannot be SQL null values.")
> Moreover, that method doesn't give me a nice way of selecting all
> constraints on a specific column, as I would have to write clauses
> like this:
>
> ... WHERE conkey[1] = blah OR conkey[2] = blah OR conkey[3] = blah OR
> conkey[4] = blah ...
>
> Can somone offer a better way?
Well if you are willing to extend contrib package intarray
to something like smallintarray
you could simply do
SELECT conname from pg_constraint where conrelid=<your table oid> and
'{blah}' ~ conkey;
Or as a quick solution create your own function
boolean isinarr(smallint,smallint[])
that performs this task, and do
SELECT conname from pg_constraint where conrelid=<your table oid> and
isinarr(blah,conkey);
>
>
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Achilleus Mantzios
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