Re: Performance improvement for joins where outer side is unique

BTW, I find this coding (first cast, then check) rather strange:

    Var *var = (Var *) ecm->em_expr;

    if (!IsA(var, Var))
        continue; /* Ignore Consts */

It's probably harmless, but I find it confusing and I can't remember
seeing it elsewhere in the code (for example clausesel.c and such) use
this style:

    ... clause is (Node*) ...

    if (IsA(clause, Var))
    {
        Var *var = (Var*)clause;
        ...
    }

or

    Var * var = NULL;

    if (! IsA(clause, Var))
        // error / continue

    var = (Var*)clause;