SQL查詢一個表中另外一個表不存在的數據

#方法一：使用 not in ,容易理解,效率低 ~執行時間爲：1.395秒~

SELECT COUNT(1) FROM ecs_goods WHERE ecs_goods.goods_id NOT IN (SELECT ecs_member_price.goods_id FROM ecs_member_price);

#方法二：使用 left join...on... , "B.ID isnull" 表示左連接之後在B.ID 字段爲 null的記錄 ~執行時間：0.739秒~

SELECT COUNT(1) FROM ecs_goods LEFT JOIN ecs_member_price ON ecs_goods.goods_id=ecs_member_price.goods_id WHERE ecs_member_price.goods_id IS NULL;

#方法三：邏輯相對複雜,但是速度最快 ~執行時間: 0.570秒~

SELECT COUNT(1) FROM  ecs_goods c WHERE (SELECT COUNT(1) AS num FROM ecs_member_price WHERE ecs_member_price.goods_id=ecs_goods.goods_id) = 0;