Question

我要选择没有任何订单或没有任何“ PAID”订单的用户：

SELECT "users".* 
FROM "users" 
LEFT OUTER JOIN orders ON orders.user_id=users.id 
WHERE (NOT (orders.state = 'paid'))

这只会返回尚未支付订单的用户，而忽略没有订单的用户。

我该如何纠正？

Answer 1

这是逻辑：

SELECT u.*
FROM "users" u LEFT JOIN
     orders o
     ON o.user_id = u.id AND o.state = 'paid'  -- match on "paid"
WHERE o.user_id IS NULL;                       -- return without a match

使用NOT EXISTS可能会更好地理解这一点：

SELECT u.*
FROM "users" u 
WHERE NOT EXISTS (SELECT 1                    -- the following does not exist
                  FROM orders o
                  WHERE o.user_id = u.id AND  -- match on the user
                        o.state = 'paid'      -- match paid state
                 );

如何选择非付费用户？

1 个答案: