MySQL中的ROW_NUMBER() [英] ROW_NUMBER() in MySQL

问题描述

MySQL中是否有复制SQL Server函数ROW_NUMBER()的好方法?

Is there a nice way in MySQL to replicate the SQL Server function ROW_NUMBER()?

例如:

SELECT 
    col1, col2, 
    ROW_NUMBER() OVER (PARTITION BY col1, col2 ORDER BY col3 DESC) AS intRow
FROM Table1

然后，例如，我可以添加一个条件以将intRow限制为1，以获得每对(col1, col2)对具有最高col3的单行.

Then I could, for example, add a condition to limit intRow to 1 to get a single row with the highest col3 for each (col1, col2) pair.

推荐答案

我想要每对(col1，col2)对具有最高col3的行.

I want the row with the single highest col3 for each (col1, col2) pair.

这是分组最大值，其中之一最常见的SQL问题(因为看起来应该很容易，但实际上并非如此).

That's a groupwise maximum, one of the most commonly-asked SQL questions (since it seems like it should be easy, but actually it kind of isn't).

我经常为null-self-join充实:

I often plump for a null-self-join:

SELECT t0.col3
FROM table AS t0
LEFT JOIN table AS t1 ON t0.col1=t1.col1 AND t0.col2=t1.col2 AND t1.col3>t0.col3
WHERE t1.col1 IS NULL;

获取表中没有其他匹配col1，col2的行具有更高col3的行." (您会注意到这一点，并且如果多行具有相同的col1，col2，col3，则大多数其他按组最大的解决方案将返回多行.如果这是一个问题，则可能需要进行一些后期处理.)

"Get the rows in the table for which no other row with matching col1,col2 has a higher col3." (You will notice this and most other groupwise-maximum solutions will return multiple rows if more than one row has the same col1,col2,col3. If that's a problem you may need some post-processing.)

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