Re: [閒聊] 每日LeetCode
練習SQL
183. Customers Who Never Order
Table: Customers
+-------------+---------+
| Column Name | Type |
+-------------+---------+
| id | int |
| name | varchar |
+-------------+---------+
Table: Orders
+-------------+------+
| Column Name | Type |
+-------------+------+
| id | int |
| customerId | int |
+-------------+------+
查出沒點餐的客人，順序不限
解:
SELECT name AS Customers FROM Customers
LEFT JOIN Orders ON Customers.id = Orders.customerId
WHERE customerId is NULL
查了一下發現有EXISTS可以用
另外可以直接SELECT另一張表當作目標，不用先組合起來
SELECT name AS Customers FROM Customers
WHERE NOT EXISTS (SELECT customerId FROM Orders WHERE Orders.CustomerId =
Customers.id)
看起來還是很爛 又查了一下發現有IN可以用
SELECT name AS Customers FROM Customers
WHERE id NOT IN (SELECT customerId FROM Orders)
好，我滿意了
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