PostgreSQL-pull_ands-pull_ors

PG pull_ands pull_ors

pull_ands() 和 pull_ors() 的就是把树状结构的 AND、OR 操作拉平.

before pull_ands()： A = 1 and B = 1 and (C = 1 and D = 1)
after pull_ands()： A = 1 and B = 1 and C = 1 and D = 1

/*
 * pull_ands
 *    Recursively flatten nested AND clauses into a single and-clause list.
 *
 * Input is the arglist of an AND clause.
 * Returns the rebuilt arglist (note original list structure is not touched).
 */
static List *
pull_ands(List *andlist)
{
    List       *out_list = NIL;
    ListCell   *arg;
    foreach(arg, andlist)
    {
        Node       *subexpr = (Node *) lfirst(arg);
        /*
         * Note: we can destructively concat the subexpression's arglist
         * because we know the recursive invocation of pull_ands will have
         * built a new arglist not shared with any other expr. Otherwise we'd
         * need a list_copy here.
         */
        if (and_clause(subexpr))
            out_list = list_concat(out_list,
                                   pull_ands(((BoolExpr *) subexpr)->args));
        else
            out_list = lappend(out_list, subexpr);
    }
    return out_list;
}
/*
 * pull_ors
 *    Recursively flatten nested OR clauses into a single or-clause list.
 *
 * Input is the arglist of an OR clause.
 * Returns the rebuilt arglist (note original list structure is not touched).
 */
static List *
pull_ors(List *orlist)
{
    List       *out_list = NIL;
    ListCell   *arg;
    foreach(arg, orlist)
    {
        Node       *subexpr = (Node *) lfirst(arg);
        /*
         * Note: we can destructively concat the subexpression's arglist
         * because we know the recursive invocation of pull_ors will have
         * built a new arglist not shared with any other expr. Otherwise we'd
         * need a list_copy here.
         */
        if (or_clause(subexpr))
            out_list = list_concat(out_list,
                                   pull_ors(((BoolExpr *) subexpr)->args));
        else
            out_list = lappend(out_list, subexpr);
    }
    return out_list;
}