MySQL query to GROUP BY multiple columns

You can use IF() to GROUP BY multiple columns. To understand the concept, let us create a table. The query to create a table is as follows
mysql> create table MultipleGroupByDemo
   -> (
   -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   -> CustomerId int,
   -> ProductName varchar(100)
   -> );
Query OK, 0 rows affected (0.59 sec)
Insert some records in the table using insert command. The query is as follows −
mysql> insert into MultipleGroupByDemo(CustomerId,ProductName) values(1000,'Product-1');
Query OK, 1 row affected (0.20 sec)
mysql> insert into MultipleGroupByDemo(CustomerId,ProductName) values(1001,'Product-2');
Query OK, 1 row affected (0.18 sec)
mysql> insert into MultipleGroupByDemo(CustomerId,ProductName) values(1001,'Product-2');
Query OK, 1 row affected (0.16 sec)
mysql> insert into MultipleGroupByDemo(CustomerId,ProductName) values(1001,'Product-2');
Query OK, 1 row affected (0.12 sec)
mysql> insert into MultipleGroupByDemo(CustomerId,ProductName) values(1002,'Product-3');
Query OK, 1 row affected (0.09 sec)
mysql> insert into MultipleGroupByDemo(CustomerId,ProductName) values(1002,'Product-3');
Query OK, 1 row affected (0.15 sec)
mysql> insert into MultipleGroupByDemo(CustomerId,ProductName) values(1003,'Product-4');
Query OK, 1 row affected (0.16 sec)
Display all records from the table using select statement. The query is as follows −
mysql> select *from MultipleGroupByDemo;
The output is as follows
+----+------------+-------------+
| Id | CustomerId | ProductName |
+----+------------+-------------+
|  1 |       1000 | Product-1   |
|  2 |       1001 | Product-2   |
|  3 |       1001 | Product-2   |
|  4 |       1001 | Product-2   |
|  5 |       1002 | Product-3   |
|  6 |       1002 | Product-3   |
|  7 |       1003 | Product-4   |
+----+------------+-------------+
7 rows in set (0.00 sec)
Here is the query to GROUP BY multiple columns
mysql> SELECT CustomerId, if( ProductName = 'Product-2', 1, 0 )
   -> FROM MultipleGroupByDemo
   -> GROUP BY ProductName , CustomerId;
The following is the output
+------------+---------------------------------------+
| CustomerId | if( ProductName = 'Product-2', 1, 0 ) |
+------------+---------------------------------------+
|       1000 |                                     0 |
|       1001 |                                     1 |
|       1002 |                                     0 |
|       1003 |                                     0 |
+------------+---------------------------------------+
4 rows in set (0.00 sec)
Here is an alternate query
mysql> select CustomerId,MAX(IF(ProductName = 'Product-2', 1,0)) from MultipleGroupByDemo group by CustomerId;
The following is the output
+------------+-----------------------------------------+
| CustomerId | MAX(IF(ProductName = 'Product-2', 1,0)) |
+------------+-----------------------------------------+
|       1000 |                                       0 |
|       1001 |                                       1 |
|       1002 |                                       0 |
|       1003 |                                       0 |
+------------+-----------------------------------------+
4 rows in set (0.00 sec)