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法学研究如何在 MySQL 中如果另一个列满足条件而对某一列中的单元格进行求和？
为此，你可以使用聚合函数 SUM() 以及 GROUP BY 子句。我们首先创建一个表 -
mysql> create table DemoTable -> ( -> EmployeeName varchar(20), -> JoiningDate date, -> Salary int -> ); Query OK, 0 rows affected (0.54 sec)
使用 insert 命令在表中插入一些记录 -
mysql> insert into DemoTable values('David','2019-11-02',400);
Query OK, 1 row affected (0.52 sec)
mysql> insert into DemoTable values('Robert','2018-11-25',100);
Query OK, 1 row affected (0.39 sec)
mysql> insert into DemoTable values('Bob','2019-12-14',600);
Query OK, 1 row affected (0.25 sec)
mysql> insert into DemoTable values('Carol','2019-11-03',300);
Query OK, 1 row affected (0.23 sec)使用 select 语句显示表中的所有记录 -
mysql> select * from DemoTable;
这将会产生以下输出 -
+--------------+-------------+--------+ | EmployeeName | JoiningDate | Salary | +--------------+-------------+--------+ | David | 2019-11-02 | 400 | | Robert | 2018-11-25 | 100 | | Bob | 2019-12-14 | 600 | | Carol | 2019-11-03 | 300 | +--------------+-------------+--------+ 4 rows in set (0.00 sec)
以下是如果另一个列满足条件而对某一列中的单元格进行求和的查询 -
mysql> select year(JoiningDate) as JoiningYear, -> month(JoiningDate) as JoiningMonth, -> sum(Salary) as Total, -> group_concat(EmployeeName) as Name -> from DemoTable -> group by JoiningYear,JoiningMonth;
这将会产生以下输出 -
+-------------+--------------+-------+-------------+ | JoiningYear | JoiningMonth | Total | Name | +-------------+--------------+-------+-------------+ | 2018 | 11 | 100 | Robert | | 2019 | 11 | 700 | David,Carol | | 2019 | 12 | 600 | Bob | +-------------+--------------+-------+-------------+ 3 rows in set (0.04 sec)
更新于： 28-Feb-2020
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