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MySQL Select Statement DISTINCT for Multiple Columns?
To understand the MySQL select statement DISTINCT for multiple columns, let us see an example and create a table. The query to create a table is as follows
mysql> create table selectDistinctDemo -> ( -> InstructorId int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> StudentId int, -> TechnicalSubject varchar(100) -> ); Query OK, 0 rows affected (0.50 sec)
Insert some records in the table using insert command. The query is as follows
mysql> insert into selectDistinctDemo(StudentId,TechnicalSubject) values(121,'Java'); Query OK, 1 row affected (0.15 sec) mysql> insert into selectDistinctDemo(StudentId,TechnicalSubject) values(121,'MongoDB'); Query OK, 1 row affected (0.16 sec) mysql> insert into selectDistinctDemo(StudentId,TechnicalSubject) values(121,'MySQL'); Query OK, 1 row affected (0.15 sec) mysql> insert into selectDistinctDemo(StudentId,TechnicalSubject) values(298,'Python'); Query OK, 1 row affected (0.11 sec) mysql> insert into selectDistinctDemo(StudentId,TechnicalSubject) values(298,'SQL Server'); Query OK, 1 row affected (0.15 sec) mysql> insert into selectDistinctDemo(StudentId,TechnicalSubject) values(397,'C#'); Query OK, 1 row affected (0.13 sec)
Display all records from the table using a select statement. The query is as follows
mysql> select *from selectDistinctDemo;
The following is the output
+--------------+-----------+------------------+ | InstructorId | StudentId | TechnicalSubject | +--------------+-----------+------------------+ | 1 | 121 | Java | | 2 | 121 | MongoDB | | 3 | 121 | MySQL | | 4 | 298 | Python | | 5 | 298 | SQL Server | | 6 | 397 | C# | +--------------+-----------+------------------+ 6 rows in set (0.00 sec)
Here is the query to use select statement DISTINCT for multiple columns
mysql> select InstructorId,StudentId,TechnicalSubject from selectDistinctDemo -> where InstructorId IN -> ( -> select max(InstructorId) from selectDistinctDemo -> group by StudentId -> ) -> order by InstructorId desc;
The following is the output
+--------------+-----------+------------------+ | InstructorId | StudentId | TechnicalSubject | +--------------+-----------+------------------+ | 6 | 397 | C# | | 5 | 298 | SQL Server | | 3 | 121 | MySQL | +--------------+-----------+------------------+ 3 rows in set (0.10 sec)
Updated on: 30-Jul-2019
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