Finding average marks of students for different subjects and display only the highest average marks in MySQL

For this, you can use subquery. Let us first create a table −

mysql> create table DemoTable
(
   StudentName varchar(40),
   StudentMarks int
);
Query OK, 0 rows affected (0.50 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable values('Adam',56);
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable values('Chris',78);
Query OK, 1 row affected (0.13 sec)
mysql> insert into DemoTable values('Adam',89);
Query OK, 1 row affected (0.13 sec)
mysql> insert into DemoTable values('Robert',98);
Query OK, 1 row affected (0.19 sec)
mysql> insert into DemoTable values('Chris',65);
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable values('Robert',34);
Query OK, 1 row affected (0.20 sec)

Display all records from the table using select statement −

mysql> select *from DemoTable;

This will produce the following output −

+-------------+--------------+
| StudentName | StudentMarks |
+-------------+--------------+
| Adam        |           56 |
| Chris       |           78 |
| Adam        |           89 |
| Robert      |           98 |
| Chris       |           65 |
| Robert      |           34 |
+-------------+--------------+
6 rows in set (0.00 sec)

Following is the query to find average marks of students and display only the highest average marks −

mysql> select max(avSal.StudentMarks)
from (select avg(StudentMarks) as `StudentMarks` from DemoTable group by StudentName) as avSal;

This will produce the following output −

+-------------------------+
| max(avSal.StudentMarks) |
+-------------------------+
|                 72.5000 |
+-------------------------+
1 row in set (0.09 sec)