Question

in my my-sql user data, there are two columns, which are u_id and u_name.

I would like to update u_name as u_id if there is no value.

UPDATE T_USER_ACCOUNT SET `u_name`=`u_id` WHERE `u_name` = 'NULL'

I ran this query but it affected 0 row.

what caused the error?

Answer 1

You shouldn’t assign (=) null to a column when you want to compare with NULL values. The correct way is:

UPDATE T_USER_ACCOUNT SET `u_name`=`u_id` WHERE `u_name` IS NULL

in your query,

UPDATE T_USER_ACCOUNT SET `u_name`=`u_id` WHERE `u_name` = 'NULL'

you are searching for u_name which has a String or VARCHAR value of NULL