Re: plan for function returning table combined with condition

You want this SQL function to be inlined, but it isn't being.
I think the reason is that (by default) it's VOLATILE, and
inline_set_returning_function doesn't like that:

     * Forget it if the function is not SQL-language or has other showstopper
     * properties.  In particular it mustn't be declared STRICT, since we
     * couldn't enforce that.  It also mustn't be VOLATILE, because that is
     * supposed to cause it to be executed with its own snapshot, rather than
     * sharing the snapshot of the calling query.  We also disallow returning
     * SETOF VOID, because inlining would result in exposing the actual result
     * of the function's last SELECT, which should not happen in that case.

So try adding STABLE to the function definition.