Using GROUP BY and MAX on multiple columns in MySQL?

To understand the GROUP BY and MAX on multiple columns, let us first create a table. The query to create a table is as follows −

mysql> create table GroupByMaxDemo
   -> (
   -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   -> CategoryId int,
   -> Value1 int,
   -> Value2 int
   -> );
Query OK, 0 rows affected (0.68 sec)

Example

Insert some records in the table using insert command. The query is as follows −

mysql> insert into GroupByMaxDemo(CategoryId, Value1,Value2) values(10,100,50);
Query OK, 1 row affected (0.15 sec)
mysql> insert into GroupByMaxDemo(CategoryId, Value1,Value2) values(10,100,70);
Query OK, 1 row affected (0.21 sec)
mysql> insert into GroupByMaxDemo(CategoryId, Value1,Value2) values(10,50,100);
Query OK, 1 row affected (0.22 sec)
mysql> insert into GroupByMaxDemo(CategoryId, Value1,Value2) values(20,180,150);
Query OK, 1 row affected (0.19 sec)

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

mysql> select *from GroupByMaxDemo;

Output

+----+------------+--------+--------+
| Id | CategoryId | Value1 | Value2 |
+----+------------+--------+--------+
|  1 |         10 |    100 |     50 |
|  2 |         10 |    100 |     70 |
|  3 |         10 |     50 |    100 |
|  4 |         20 |    180 |    150 |
+----+------------+--------+--------+
4 rows in set (0.00 sec)

Example

The following is the query to use GROUP BY and MAX on multiple columns −

mysql> select tbl2.CategoryId, tbl2.Value1, max(tbl2.Value2)
   -> from
   -> (
   -> select CategoryId, max(Value1) as `Value1`
   -> from GroupByMaxDemo
   -> group by CategoryId
   -> ) tbl1
   -> inner join GroupByMaxDemo tbl2 on tbl2.CategoryId = tbl1.CategoryId and tbl2.Value1 = tbl1.Value1
   -> group by tbl2.CategoryId, tbl2.Value1;

Output

+------------+--------+------------------+
| CategoryId | Value1 | max(tbl2.Value2) |
+------------+--------+------------------+
|         10 |    100 |               70 |
|         20 |    180 |              150 |
+------------+--------+------------------+
2 rows in set (0.00 sec)

Samual Sam

Published on 19-Mar-2019 07:51:01

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