Replace Values in a MySQL Table

To replace values in a table, use the CASE statement. To understand the concept, let us create a table. The query to create a table is as follows

mysql> create table replaceValueDemo
   -> (
   -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   -> Name varchar(10),
   -> isGreaterThan18 varchar(10)
   -> );
Query OK, 0 rows affected (0.49 sec)

Insert some records in the table using insert command.

The query is as follows

mysql> insert into replaceValueDemo(Name,isGreaterThan18) values('John','YES');
Query OK, 1 row affected (0.24 sec)
mysql> insert into replaceValueDemo(Name,isGreaterThan18) values('Carol','NO');
Query OK, 1 row affected (0.16 sec)
mysql> insert into replaceValueDemo(Name,isGreaterThan18) values('Mike','YES');
Query OK, 1 row affected (0.20 sec)
mysql> insert into replaceValueDemo(Name,isGreaterThan18) values('Bob','YES');
Query OK, 1 row affected (0.17 sec)
mysql> insert into replaceValueDemo(Name,isGreaterThan18) values('Larry','NO');
Query OK, 1 row affected (0.09 sec)
mysql> insert into replaceValueDemo(Name,isGreaterThan18) values('David','NO');
Query OK, 1 row affected (0.11 sec)
mysql> insert into replaceValueDemo(Name,isGreaterThan18) values('James','DONOTKNOW');
Query OK, 1 row affected (0.14 sec)
mysql> insert into replaceValueDemo(Name,isGreaterThan18) values('Robert','DONOTKNOW');
Query OK, 1 row affected (0.13 sec)

Display all records from the table using select statement.

The query is as follows

mysql> select *from replaceValueDemo;

The following is the output

+----+--------+-----------------+
| Id | Name   | isGreaterThan18 |
+----+--------+-----------------+
| 1  | John   | YES             |
| 2  | Carol  | NO              |
| 3  | Mike   | YES             |
| 4  | Bob    | YES             |
| 5  | Larry  | NO              |
| 6  | David  | NO              |
| 7  | James  | DONOTKNOW       |
| 8  | Robert | DONOTKNOW       |
+----+--------+-----------------+
8 rows in set (0.00 sec)

Here is the query to replace values in a MySQL table

mysql> update replaceValueDemo set isGreaterThan18=case when isGreaterThan18='YES' THEN 'NO' ELSE 'YES' END
   -> where isGreaterThan18 IN('YES','NO');
Query OK, 6 rows affected (0.19 sec)
Rows matched: 6 Changed: 6 Warnings: 0

Let us check the table records once again.

The query is as follows

mysql> select *from replaceValueDemo;

The following is the output with the replaced values

+----+--------+-----------------+
| Id | Name   | isGreaterThan18 |
+----+--------+-----------------+
| 1  | John   | NO              |
| 2  | Carol  | YES             |
| 3  | Mike   | NO              |
| 4  | Bob    | NO              |
| 5  | Larry  | YES             |
| 6  | David  | YES             |
| 7  | James  | DONOTKNOW       |
| 8  | Robert | DONOTKNOW       |
+----+--------+-----------------+
8 rows in set (0.00 sec)