Re: [SQL] how can tell if a column is a primary key?

"D'Arcy" "J.M." Cain <darcy@druid.net> writes:
> Here's another FAQ but one that no one has ever answered that I know of.
> How do I generalize the above query so that it returns information on
> all the elements of complex keys?

indkey and indclass are type int28 and oid8 respectively, which are
almost like 8-element arrays, except that for historical reasons they
index from 0 not 1.  So instead of pg_index.indkey[0] = pg_attribute.attnum
write pg_index.indkey[1] = pg_attribute.attnum to find attributes that
are secondary index columns, [2] for tertiary, etc.  Unused positions
in indkey[] are filled with zeroes.

If you have code on the client side it'd probably make most sense just
to pull back the whole value of indkey[] and then issue separate SELECTs
to find out what the referenced attributes are, instead of probing 8
times to see if you get anything...

BTW, if indproc is nonzero then you are looking at a functional index,
and in that case the indkey[] array describes the arguments to the
function; there is only one index column, namely the function result.
        regards, tom lane