分组并取得最后一行 [英] Group by and get the last row

问题描述

当我使用

  SELECT * FROM报告时WHERE staff ='$ username'GROUP BY taskid 
  

在我的查询中，我得到该组第一行的结果。

我需要添加什么来获得该组最后一行的结果？

最后一行意味着id大于另一行的结果

我尝试添加

  ORDER BY id DESC 
  

或

  ORDER BY id 
  

但它没有返回预期的结果。

解决方案

您正在使用不带任何聚合函数的函数组。您可能想通过改为执行一个订单（在查询中没有分组）：

  SELECT * FROM reports WHERE staff =' $ username'order BY taskid desc; 
  

Group By函数通常用于在特定列上使用聚合函数（如获得平均行值或总和）等。如果您没有使用任何聚合函数，那么使用Group By将不会执行任何操作。

如果您只想从查询中获取一行，则可以添加一个限制子句像这样：

$ p $ SELECT * FROM reports WHERE staff ='$ username'order BY taskid desc limit 1;


When I used the

SELECT * FROM reports WHERE staff='$username' GROUP BY taskid

on my query, I get a result of the first row from that group.

What do I need to add to get the result from the last row of that group?

last row means having id greater than the other row from that group.

I tried adding

ORDER BY id DESC 

or

ORDER BY id

but it did not return the intended result.

解决方案

You are using a group by function without any aggregate functions. You probably want to do an order by instead (No group by in the query):

SELECT * FROM reports WHERE staff='$username' order BY taskid desc;

Group By functions are commonly used when you want to use an aggregate function on a particular column (such as get an average row value, or a sum) and the like. If you are not using any aggregate function, then using Group By will not do anything.

If you only want to get one row from the query you can add a limit clause like this:

SELECT * FROM reports WHERE staff='$username' order BY taskid desc limit 1;

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