Function canonicalize_ec_expression

src/backend/optimizer/path/equivclass.c:499–539

* canonicalize_ec_expression * * This function ensures that the expression exposes the expected type and * collation, so that it will be equal() to other equivalence-class expressions * that it ought to be equal() to. * * The rule for datatypes is that the exposed type should match what it would * be for an input to an operator of the EC's opfamilies; which is usually * the declared input

 * right answer for a sort key.)
 */
Expr *
canonicalize_ec_expression(Expr *expr, Oid req_type, Oid req_collation)
{
	Oid			expr_type = exprType((Node *) expr);

	/*
	 * For a polymorphic-input-type opclass, just keep the same exposed type.
	 * RECORD opclasses work like polymorphic-type ones for this purpose.
	 */
	if (IsPolymorphicType(req_type) || req_type == RECORDOID)
		req_type = expr_type;

	/*
	 * No work if the expression exposes the right type/collation already.
	 */
	if (expr_type != req_type ||
		exprCollation((Node *) expr) != req_collation)
	{
		/*
		 * If we have to change the type of the expression, set typmod to -1,
		 * since the new type may not have the same typmod interpretation.
		 * When we only have to change collation, preserve the exposed typmod.
		 */
		int32		req_typmod;

		if (expr_type != req_type)
			req_typmod = -1;
		else
			req_typmod = exprTypmod((Node *) expr);

		/*
		 * Use applyRelabelType so that we preserve const-flatness.  This is
		 * important since eval_const_expressions has already been applied.
		 */
		expr = (Expr *) applyRelabelType((Node *) expr,
										 req_type, req_typmod, req_collation,
										 COERCE_IMPLICIT_CAST, -1, false);
	}

	return expr;
}

/*
 * add_eq_member - build a new EquivalenceMember and add it to an EC