Function arraycontsel

src/backend/utils/adt/array_selfuncs.c:241–316

* arraycontsel -- restriction selectivity for array @>, &&, <@ operators */

 * arraycontsel -- restriction selectivity for array @>, &&, <@ operators
 */
Datum
arraycontsel(PG_FUNCTION_ARGS)
{
	PlannerInfo *root = (PlannerInfo *) PG_GETARG_POINTER(0);
	Oid			operator = PG_GETARG_OID(1);
	List	   *args = (List *) PG_GETARG_POINTER(2);
	int			varRelid = PG_GETARG_INT32(3);
	VariableStatData vardata;
	Node	   *other;
	bool		varonleft;
	Selectivity selec;
	Oid			element_typeid;

	/*
	 * If expression is not (variable op something) or (something op
	 * variable), then punt and return a default estimate.
	 */
	if (!get_restriction_variable(root, args, varRelid,
								  &vardata, &other, &varonleft))
		PG_RETURN_FLOAT8(DEFAULT_SEL(operator));

	/*
	 * Can't do anything useful if the something is not a constant, either.
	 */
	if (!IsA(other, Const))
	{
		ReleaseVariableStats(vardata);
		PG_RETURN_FLOAT8(DEFAULT_SEL(operator));
	}

	/*
	 * The "&&", "@>" and "<@" operators are strict, so we can cope with a
	 * NULL constant right away.
	 */
	if (((Const *) other)->constisnull)
	{
		ReleaseVariableStats(vardata);
		PG_RETURN_FLOAT8(0.0);
	}

	/*
	 * If var is on the right, commute the operator, so that we can assume the
	 * var is on the left in what follows.
	 */
	if (!varonleft)
	{
		if (operator == OID_ARRAY_CONTAINS_OP)
			operator = OID_ARRAY_CONTAINED_OP;
		else if (operator == OID_ARRAY_CONTAINED_OP)
			operator = OID_ARRAY_CONTAINS_OP;
	}

	/*
	 * OK, there's a Var and a Const we're dealing with here.  We need the
	 * Const to be an array with same element type as column, else we can't do
	 * anything useful.  (Such cases will likely fail at runtime, but here
	 * we'd rather just return a default estimate.)
	 */