我们可以使用具有相同字段名的 group by 和 where

问题描述

我有一个要求，比如必须提取用户选择的日期范围内的所有记录，选择从 2011 年 1 月 15 日到 2011 年 8 月 20 日开始的所有员工，并按日期分组.

I have a requirement like have to pull all records in the date range the user selected, selecting all employees who started from 15-Jan-2011 to 20-Aug-2011 and group by date.

我应该如何为此编写 SQL 查询:

How should I write SQL query for this:

  SELECT *
    FROM employees 
   WHERE startdate >= '15-jan-2011' 
     AND startdate <= '20-aug-2011'
GROUP BY startdate

推荐答案

绝对可以.这将导致过滤日期范围内的记录，然后按有数据的每一天对其进行分组.

Absolutely. It will result in filtering the records on your date range and then grouping it by each day where there is data.

应该注意的是，您只能选择开始日期，然后选择您正在计算的任何聚合.否则，它应该可以正常工作.

It should be noted that you will only be able to select the startdate and then whatever aggregates you're calculating. Otherwise, it should work perfectly fine.

例如，此查询将为您提供每个开始日期的员工数:

For example, this query will give you a count of employees for each startdate:

SELECT startdate, count(*)
FROM employees 
WHERE startdate >= '15-jan-2011' 
      AND startdate <= '20-aug-2011'
GROUP BY startdate

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