Question

我需要在代码的特定区域锁定一个表。

所以我锁定了我的桌子：

LOCK TABLE christmas_game WRITE;

工作正常。

现在我需要在这张桌子上SELECT，所以我这样做：

SELECT SQL_NO_CACHE prize
FROM christmas_game
WHERE user_id = {$this->user_id}
ORDER BY created_at DESC
LIMIT 2

哪个也好。但由于某种原因，这根本不起作用：

SELECT prize
FROM christmas_game
WHERE DATE(created_at) = CURDATE()
AND user_id != '{$uniqId}'
GROUP BY prize
UNION
SELECT prize
FROM christmas_game
WHERE user_id = {$user->user_id}
AND user_id != '{$uniqId}'
AND prize IN ('promo_1', 'promo_2')

我收到错误消息：Table 'christmas_game' was not locked with LOCK TABLES。显然UNION在这里有问题，因为没有它，两个查询都可以正常工作。

为什么？

Answer 1

您必须锁定两个表，并且不能锁定相同表的两次。

解决方案是为表添加别名：

LOCK TABLE christmas_game as table_locked_game_1 WRITE, christmas_game as table_locked_game_2 write;

然后在您的联盟中添加相同的别名：

    SELECT prize 
    FROM christmas_game as table_locked_game_1 
    WHERE DATE(created_at) = CURDATE() GROUP BY prize 
UNION 
    SELECT prize FROM christmas_game as table_locked_game_2 
    WHERE user_id = 81 
    AND prize IN ('promo_1', 'promo_2')

在LOCK TABLES表示表未锁定后，在UNION查询上进行SELECT

1 个答案: