MySQL 合并选择?
mysqlmysqli database
要合并选择，您需要使用 GROUP BY 子句。为了理解这个概念，让我们创建一个表。创建表的查询如下 −
mysql> create table MergingSelectDemo -> ( -> RoomServicesId int, -> RoomId int, -> ServiceId int -> ); Query OK, 0 rows affected (1.98 sec)
现在，您可以使用 insert 命令在表中插入一些记录。查询如下 −
mysql> insert into MergingSelectDemo values(10,10,10); Query OK, 1 row affected (0.29 sec) mysql> insert into MergingSelectDemo values(20,10,20); Query OK, 1 row affected (0.22 sec) mysql> insert into MergingSelectDemo values(30,10,30); Query OK, 1 row affected (0.14 sec) mysql> insert into MergingSelectDemo values(50,10,50); Query OK, 1 row affected (0.19 sec) mysql> insert into MergingSelectDemo values(110,20,20); Query OK, 1 row affected (0.14 sec) mysql> insert into MergingSelectDemo values(120,20,30); Query OK, 1 row affected (0.37 sec)
使用 select 语句显示表中的所有记录。查询如下 −
mysql> select *from MergingSelectDemo;
以下是输出 −
+----------------+--------+-----------+ | RoomServicesId | RoomId | ServiceId | +----------------+--------+-----------+ | 10 | 10 | 10 | | 20 | 10 | 20 | | 30 | 10 | 30 | | 50 | 10 | 50 | | 110 | 20 | 20 | | 120 | 20 | 30 | +----------------+--------+-----------+ 6 rows in set (0.00 sec)
这是合并选择的查询 −
mysql> select RoomId from MergingSelectDemo -> where ServiceId IN(10,20,30) -> group by RoomId -> HAVING COUNT(*)=3;
以下是输出 −
+--------+ | RoomId | +--------+ | 10 | +--------+ 1 row in set (0.15 sec)
