Function predicate_implied_by

src/backend/optimizer/util/predtest.c:155–184

* predicate_implied_by * Recursively checks whether the clauses in clause_list imply that the * given predicate is true. * * We support two definitions of implication: * * "Strong" implication: A implies B means that truth of A implies truth of B. * We use this to prove that a row satisfying one WHERE clause or index * predicate must satisfy another one. * * "Weak" implication: A imp

 * Immutability of functions in the clause_list is checked here, if necessary.
 */
bool
predicate_implied_by(List *predicate_list, List *clause_list,
					 bool weak)
{
	Node	   *p,
			   *c;

	if (predicate_list == NIL)
		return true;			/* no predicate: implication is vacuous */
	if (clause_list == NIL)
		return false;			/* no restriction: implication must fail */

	/*
	 * If either input is a single-element list, replace it with its lone
	 * member; this avoids one useless level of AND-recursion.  We only need
	 * to worry about this at top level, since eval_const_expressions should
	 * have gotten rid of any trivial ANDs or ORs below that.
	 */
	if (list_length(predicate_list) == 1)
		p = (Node *) linitial(predicate_list);
	else
		p = (Node *) predicate_list;
	if (list_length(clause_list) == 1)
		c = (Node *) linitial(clause_list);
	else
		c = (Node *) clause_list;

	/* And away we go ... */
	return predicate_implied_by_recurse(c, p, weak);
}

/*
 * predicate_refuted_by