MySQL 使用单个查询从两个表中进行 SELECT
mysqlmysqli database更新于 2024/4/4 9:38:00
使用 UNION 从两个表中进行选择。让我们首先创建一个表 −
mysql> create table DemoTable1 ( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, FirstName varchar(20) ); Query OK, 0 rows affected (0.90 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable1(FirstName) values('Chris') ;
Query OK, 1 row affected (0.19 sec)
mysql> insert into DemoTable1(FirstName) values('Adam');
Query OK, 1 row affected (0.21 sec)
mysql> insert into DemoTable1(FirstName) values('Sam');
Query OK, 1 row affected (0.16 sec)
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 −
+----+-----------+ | Id | FirstName | +----+-----------+ | 1 | Chris | | 2 | Adam | | 3 | Sam | +----+-----------+ 3 rows in set (0.00 sec)
以下是创建第二个表的查询 −
mysql> create table DemoTable2( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, FirstName varchar(20) ); Query OK, 0 rows affected (1.75 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable2(FirstName) values('John');
Query OK, 1 row affected (0.18 sec)
mysql> insert into DemoTable2(FirstName) values('Tom');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable2(FirstName) values('Bob');
Query OK, 1 row affected (0.50 sec)
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 −
+----+-----------+ | Id | FirstName | +----+-----------+ | 1 | John | | 2 | Tom | | 3 | Bob | +----+-----------+ 3 rows in set (0.00 sec)
以下是使用 MySQL UNION 从两个表中选择的查询 −
mysql> (select *from DemoTable1) union (select *from DemoTable2) order by FirstName;
这将产生以下输出 −
+----+-----------+ | Id | FirstName | +----+-----------+ | 2 | Adam | | 3 | Bob | | 1 | Chris | | 1 | John | | 3 | Sam | | 2 | Tom | +----+-----------+ 6 rows in set (0.00 sec)
