MySQL query to select average from distinct column of table?

For getting average, use AVG() and use it with DISTINCT to calculate from distinct records. Let us first create a table −

mysql> create table DemoTable1934
   (
   StudentName varchar(20),
   StudentMarks int
   );
Query OK, 0 rows affected (0.00 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable1934 values('Chris',56);
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1934 values('Chris',56);
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1934 values('David',78);
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1934 values('David',78);
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1934 values('Carol',45);
Query OK, 1 row affected (0.00 sec)

Display all records from the table using select statement −

mysql> select * from DemoTable1934;

This will produce the following output −

+-------------+--------------+
| StudentName | StudentMarks |
+-------------+--------------+
| Chris       |           56 |
| Chris       |           56 |
| David       |           78 |
| David       |           78 |
| Carol       |           45 |
+-------------+--------------+
5 rows in set (0.00 sec)

Here is the query to select average from distinct column of table −

mysql> select avg(tbl.StudentMarks)
   from
   (
   select distinct StudentName,StudentMarks
   from DemoTable1934
   ) as tbl;

This will produce the following output −

+-----------------------+
| avg(tbl.StudentMarks) |
+-----------------------+
|               59.6667 |
+-----------------------+
1 row in set (0.00 sec)