Merge Rows in MySQL and Display Highest Corresponding Value

For this, use aggregate function MAX() along with the GROUP BY clause. Let us first create a table −

mysql> create table DemoTable
(
   Id int,
   Value1 int,
   Value2 int,
   Value3 int,
   Value4 int
);
Query OK, 0 rows affected (0.61 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable(Id,Value4) values(100,30);
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable(Id,Value1,Value2,Value3) values(100,20,60,40);
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable(Id,Value2,Value3,Value4) values(100,90,100,110);
Query OK, 1 row affected (0.10 sec)

Display all records from the table using select statement −

mysql> select *from DemoTable;

This will produce the following output −

+------+--------+--------+--------+--------+
| Id   | Value1 | Value2 | Value3 | Value4 |
+------+--------+--------+--------+--------+
| 100  | NULL   | NULL   | NULL   | 30     |
| 100  | 20     | 60     | 40     | NULL   |
| 100  | NULL   | 90     | 100    | 110    |
+------+--------+--------+--------+--------+
3 rows in set (0.00 sec)

Following is the query to merge rows if Id is the same and display the highest corresponding value from other columns −

mysql> select Id,max(Value1) as Value1,max(Value2) as Value2,max(Value3) as Value3,max(Value4) as Value4
from DemoTable
group by Id;

This will produce the following output −

+------+--------+--------+--------+--------+
| Id   | Value1 | Value2 | Value3 | Value4 |
+------+--------+--------+--------+--------+
| 100  | 20     | 90     | 100    | 110    |
+------+--------+--------+--------+--------+
1 row in set (0.00 sec)