Select distinct values from three columns and display in a single column with MySQL

For this, use UNION more than once in a single MySQL query. Let us first create a table −

mysql> create table DemoTable    -> (    -> Value1 int,    -> Value2 int,    -> Value3 int    -> ); Query OK, 0 rows affected (0.69 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable values(20,null,null); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable values(20,null,null); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable values(20,null,null); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable values(10,null,null); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable values(80,20,100); Query OK, 1 row affected (0.09 sec) mysql> insert into DemoTable values(10,null,null); Query OK, 1 row affected (0.16 sec)

Display all records from the table using select statement −

mysql> select *from DemoTable;

This will produce the following output −

+--------+--------+--------+ | Value1 | Value2 | Value3 | +--------+--------+--------+ |     20 |   NULL |   NULL | |     20 |   NULL |   NULL | |     20 |   NULL |   NULL | |     10 |   NULL |   NULL | |     80 |     20 |    100 | |     10 |   NULL |   NULL | +--------+--------+--------+ 6 rows in set (0.00 sec)

Following is the query to select distinct values from 3 columns into 1 −

mysql> select *from    -> (    -> select Value1 as AllValue from DemoTable    -> union    -> select Value2 as AllValue from DemoTable    -> union    -> select Value3 as AllValue from DemoTable    -> ) tbl where AllValue IS NOT NULL    -> order by AllValue;

This will produce the following output −

+----------+ | AllValue | +----------+ |       10 | |       20 | |       80 | |      100 | +----------+ 4 rows in set (0.00 sec)