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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.
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