Select from another column if selected value is '0' in MySQL?

For this, use IF() in MySQL. The syntax is as follows −

select IF(yourColumnName1=0,yourColumnName2,yourColumnName1) as anyAliasName
from yourTableName;

Let us create a table −

mysql> create table demo30
−> (
−> id int not null auto_increment primary key,
−> value int,
−> original_value int
−> )
−> ;
Query OK, 0 rows affected (1.87 sec)

Insert some records into the table with the help of insert command −

mysql> insert into demo30(value,original_value) values(50,10);
Query OK, 1 row affected (0.10 sec)

mysql> insert into demo30(value,original_value) values(1000,0);
Query OK, 1 row affected (0.13 sec)

mysql> insert into demo30(value,original_value) values(0,40);
Query OK, 1 row affected (0.15 sec)

mysql> insert into demo30(value,original_value) values(30,0);
Query OK, 1 row affected (0.09 sec)

Display records from the table using select statement −

mysql> select *from demo30;

This will produce the following output −

+----+-------+----------------+
| id | value | original_value |
+----+-------+----------------+
| 1  | 50    | 10             |
| 2  | 1000  | 0              |
| 3  | 0     | 40             |
| 4  | 30    | 0              |
+----+-------+----------------+
4 rows in set (0.00 sec)

Following is the query to select from another column if selected value is '0' in MySQL −

mysql> select id, if(original_value= 0,value,original_value) as Result
−> from demo30;

This will produce the following output −

+----+--------+
| id | Result |
+----+--------+
|  1 | 10     |
|  2 | 1000   |
|  3 | 40     |
|  4 | 30     |
+----+--------+
4 rows in set (0.00 sec)