MySQL 查询优化 - 避免子查询

Question

我需要更新表中的一些行，为简单起见，称为“三”。

我选择要使用此查询更新的列:

SELECT one.id
FROM one 
    JOIN `two` ON ( one.id = two.page )
    JOIN `three` ON ( one.id = three.item )
WHERE two.level = 1
    AND  two.item = (SELECT item FROM two WHERE page = 5 AND level = 1 ) 
    AND three.position > (SELECT position FROM three WHERE item = 5 ) 
ORDER BY three.position

现在我用我得到的 id 调用更新查询。

是否有机会消除子查询？

编辑(在梅兰妮评论之后):

表“一”:

|id|text|

表“二”:

|id|item|page|level|

表“三”:

|item|position|

所以当我运行查询时

SELECT item FROM two WHERE page = 5 AND level = 1

它将返回 f.ex 1 并且最终的 WHERE 子句将是:

two.item = 1 AND two.level = 1

这与以下内容不同:

two.level = 1 and two.page = 5

我有表一 - 一些文本和一些 one.id。我需要更新表三中位置高于我的项目(例如 id = 5)的所有项目。但这些项目在表二中也应具有相同的two.item，其中two.page = one.id且level = 1

很抱歉描述不准确。

Answer 1

您应该能够通过联接替换这些子查询:

SELECT one.id
FROM one 
    JOIN `two2` ON (two2.page = 5 AND two2.level = 1)
    JOIN `two` ON ( one.id = two.page AND two.item = two2.item )
    JOIN `three2` ON ( three.item = 5)
    JOIN `three` ON ( one.id = three.item AND three.position > three2.position)
WHERE two.level = 1
ORDER BY three.position