MySQL Merge selects together?

To merge selects together, you need to use GROUP BY clause. To understand the concept, let us create a table. The query to create a table is as follows −

mysql> create table MergingSelectDemo
   -> (
   -> RoomServicesId int,
   -> RoomId int,
   -> ServiceId int
   -> );
Query OK, 0 rows affected (1.98 sec)

Now you can insert some records in the table using insert command. The query is as follows −

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)

Display all records from the table using select statement. The query is as follows −

mysql> select *from MergingSelectDemo;

The following is the output −

+----------------+--------+-----------+
| 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)

Here is the query to merge select together −

mysql> select RoomId from MergingSelectDemo
   -> where ServiceId IN(10,20,30)
   -> group by RoomId
   -> HAVING COUNT(*)=3;

The following is the output −

+--------+
| RoomId |
+--------+
|     10 |
+--------+
1 row in set (0.15 sec)