How to update empty string to NULL in MySQL?

For this, use LENGTH(), since if the length is 0 that would mean the string is empty. After finding, you can set it to NULL using the SET clause in the UPDATE command. Let us first create a table −

mysql> create table DemoTable (    Name varchar(50) ); Query OK, 0 rows affected (0.68 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable values('Chris'); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable values(''); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable values('David'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable values(''); Query OK, 1 row affected (0.15 sec)

Display all records from the table using select statement −

mysql> select *from DemoTable;

This will produce the following output −

+-------+ | Name | +-------+ | Chris | | | | David | | | +-------+ 4 rows in set (0.00 sec)

Following is the query to update empty string to NULL −

mysql> update DemoTable set Name=NULL where length(Name)=0; Query OK, 2 rows affected (0.12 sec) Rows matched: 2 Changed: 2 Warnings: 0

Let us check the table records once again −

mysql> select *from DemoTable;

This will produce the following output −

+-------+ | Name | +-------+ | Chris | | NULL | | David | | NULL | +-------+ 4 rows in set (0.00 sec)