Question

我有这个数据库查询

SELECT *
FROM (`metadata` im)
INNER JOIN `content` ic ON `im`.`rev_id`  = `ic`.`rev_id`
WHERE `im`.`id` = '00039'
AND `current_revision` = 1
ORDER BY `timestamp` DESC
LIMIT 5, 5

查询将结果中的总行数限制为5.我希望将左表metadata限制为5而不限制整个结果集。

我该如何撰写查询？

Answer 1

如果你考虑一下你想要做什么，你实际上并没有针对metadata进行选择。

您需要首先进行子查询。

尝试：

SELECT *
FROM ((select * from metadata limit 5) im)
INNER JOIN `content` ic ON `im`.`rev_id`  = `ic`.`rev_id`
WHERE `im`.`id` = '00039'
AND `current_revision` = 1
ORDER BY `timestamp` DESC

Answer 2

嗯，我认为你的意思是LEFT JOIN尝试使用LEFT JOIN代替INNER JOIN

    SELECT DISTINCT *
    FROM (`metadata` im)
    INNER JOIN `content` ic ON `im`.`rev_id`  = `ic`.`rev_id`
    WHERE `im`.`id` = '00039'
    AND `current_revision` = 1
    ORDER BY `timestamp` DESC
    LIMIT 5, 5

Answer 3

这是另一种可能的方法：

SET @serial=0;
SET @thisid=0;

SELECT 
   @serial := IF((@thisid != im.id), @serial + 1, @serial), 
   @thisid := im.id,
   * 
FROM (`metadata` im)
WHERE `im`.`id` = '00039'
AND `current_revision` = 1
AND @serial < 5
ORDER BY `timestamp` DESC

未经测试。如果您遇到问题，请告诉我 - 我可以详细说明。

MySQL内部加入LIMIT到左表

3 个答案: