MYSQL 查詢的字段名寫錯都能執行？

錯誤字段在註釋3，c_id是要查詢的派生表中惟一的字段，但開始我寫成了c_sid 都能執行。

SELECT
	*
FROM
	(
	SELECT
		*
	FROM
		t_product
	WHERE
		c_sid	IN
		(#3，僅僅須要在這設置一個別名而已
			SELECT
				**c_id**
			FROM
				(#二、找出知足1,同時指定地區的5個隨機商鋪ID
					SELECT
						c_id
					FROM
						t_shops
					WHERE
						c_id IN
						(#一、找出商品表中有商鋪ID的商鋪ID	
						SELECT
							c_sid
						FROM
							t_product
						WHERE
							c_sid !=""						
						)
					AND
						c_ditclass=17
					ORDER BY
						RAND()
					LIMIT
						5				
				)
				AS
				result1
		)
	ORDER BY
		RAND()
	)
	AS
	result2
GROUP BY
	c_sid