How to implement MAX(distinct…) in MySQL and what is the difference without using DISTINCT?

Let us see the first syntax, which uses DISTINCT in MAX() −

select max(DISTINCT yourColumnName) from yourTableName;

The second syntax is as follows. It isn’t using DISTINCT −

select max( yourColumnName) from yourTableName;

NOTE − Both the above queries give the same result with or without a DISTINCT keyword. MySQL internally converts MAX(yourColumnName) to DISTINCT keyword.

Let us now see an example and create a table −

mysql> create table DemoTable
(
   Number int
);
Query OK, 0 rows affected (1.50 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable values(80);
Query OK, 1 row affected (0.09 sec)
mysql> insert into DemoTable values(88);
Query OK, 1 row affected (0.13 sec)
mysql> insert into DemoTable values(78);
Query OK, 1 row affected (0.10 sec)
mysql> insert into DemoTable values(88);
Query OK, 1 row affected (0.10 sec)
mysql> insert into DemoTable values(68);
Query OK, 1 row affected (0.09 sec)
mysql> insert into DemoTable values(88);
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 −

+--------+
| Number |
+--------+
|     80 |
|     88 |
|     78 |
|     88 |
|     68 |
|     88 |
+--------+
6 rows in set (0.00 sec)

CASE 1 − Following is the query to implement MAX(DISTINCT..) −

mysql> select max(DISTINCT Number) from DemoTable;

This will produce the following output −

+----------------------+
| max(DISTINCT Number) |
+----------------------+
|                   88 |
+----------------------+
1 row in set (0.00 sec)

CASE 2 − Following is the query to implement MAX() without DISTINCT −

mysql> select max(Number) from DemoTable;

This will produce the following output −

+-------------+
| max(Number) |
+-------------+
|          88 |
+-------------+
1 row in set (0.07 sec)

As you can see above, both of them give the same result.