在 MySQL 中用条件连接两个表?
mysqlmysqli database
要连接两个表，请在 MySQL 中使用 UNION ALL。让我们创建一个表 −
mysql> create table DemoTable1 ( Id int, FirstName varchar(20) ); Query OK, 0 rows affected (1.52 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable1 values(10,'John'); Query OK, 1 row affected (0.28 sec) mysql> insert into DemoTable1 values(20,'Carol'); Query OK, 1 row affected (0.28 sec)
使用 select 语句显示表中的所有记录 −
mysql> select *from DemoTable1;
输出
+------+-----------+ | Id | FirstName | +------+-----------+ | 10 | John | | 20 | Carol | +------+-----------+ 2 rows in set (0.00 sec)
Create second table.
mysql> create table DemoTable2 ( Id int, FirstName varchar(20) ); Query OK, 0 rows affected (1.22 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable2 values(20,'David'); Query OK, 1 row affected (1.28 sec) mysql> insert into DemoTable2 values(40,'Chris'); Query OK, 1 row affected (0.38 sec)
使用 select 语句显示表中的所有记录 −
mysql> select *from DemoTable2;
输出
+------+-----------+ | Id | FirstName | +------+-----------+ | 20 | David | | 40 | Chris | +------+-----------+ 2 rows in set (0.00 sec)
以下是连接两个表的查询 −
mysql> select *from DemoTable1 where Id=20 union all select *from DemoTable2 where Id=20;
输出
+------+-----------+ | Id | FirstName | +------+-----------+ | 20 | Carol | | 20 | David | +------+-----------+ 2 rows in set (0.43 sec)
