一个查询从MySQL中的不同表中获取计数的总和？
要从不同的表中获取计数总和，请使用UNIONALL。让我们首先创建一个表-
mysql> create table DemoTable1 -> ( -> Id int, -> Name varchar(30) -> );
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable1 values(10,'Chris Brown'); mysql> insert into DemoTable1 values(20,'David Miller'); mysql> insert into DemoTable1 values(30,'John Adam');
使用select语句显示表中的所有记录-
mysql> select *from DemoTable1;
输出结果
+------+--------------+ | Id | Name | +------+--------------+ | 10 | Chris Brown | | 20 | David Miller | | 30 | John Adam | +------+--------------+ 3 rows in set (0.00 sec)
以下是创建第二个表的查询-
mysql> create table DemoTable2 -> ( -> Amount int -> );
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable2 values(100); mysql> insert into DemoTable2 values(200); mysql> insert into DemoTable2 values(300);
使用select语句显示表中的所有记录-
mysql> select *from DemoTable2;
输出结果
+--------+ | Amount | +--------+ | 100 | | 200 | | 300 | +--------+ 3 rows in set (0.00 sec)
这是如何在单个查询中从不同表中获取计数总和-
mysql> select sum(AllCount) AS Total_Count -> from -> ( -> (select count(*) AS AllCount from DemoTable1) -> union all -> (select count(*) AS AllCount from DemoTable2) -> )t;
输出结果
+-------------+ | Total_Count | +-------------+ | 6 | +-------------+ 1 row in set (0.03 sec)