MySQL查询对多个表中的行进行计数
让我们首先创建一个表-
mysql> create table DemoTable1 (FirstName varchar(100));
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable1 values('Bob');
mysql> insert into DemoTable1 values('James');
mysql> insert into DemoTable1 values('John');
mysql> insert into DemoTable1 values('David');使用select语句显示表中的所有记录-
mysql> select *from DemoTable1;
这将产生以下输出-
+-----------+ | FirstName | +-----------+ | Bob | | James | | John | | David | +-----------+ 4 rows in set (0.00 sec)
这是创建第二个表的查询-
mysql> create table DemoTable2 (Marks int);
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable2 values(98); mysql> insert into DemoTable2 values(89); mysql> insert into DemoTable2 values(67); mysql> insert into DemoTable2 values(34); mysql> insert into DemoTable2 values(32); mysql> insert into DemoTable2 values(42);
使用select语句显示表中的所有记录-
mysql> select *from DemoTable2;
这将产生以下输出-
+-------+ | Marks | +-------+ | 98 | | 89 | | 67 | | 34 | | 32 | | 42 | +-------+ 6 rows in set (0.00 sec)
这是对多个表中的行进行计数的查询-
mysql> select (select count(*) from DemoTable1) AS First_Table_Row, (select count(*) from DemoTable2) AS Second_Table_Row;
这将产生以下输出-
+-----------------+------------------+ | First_Table_Row | Second_Table_Row | +-----------------+------------------+ | 4 | 6 | +-----------------+------------------+ 1 row in set (0.00 sec)