Why would rows match but not be changed with a mysql update statement?

Question

I'm used to MSSQL, not Mysql, so sorry for this probably stupid question. I'm trying update my password for a backup database I'm getting setup by running the following query:

update users set password = md5('pass') where username = 'admin'

When I run this it says

Query OK, 0 rows affected (0.01 sec) Rows matched: 1 Changed: 0 Warnings: 0

Why is a row matching but not changing?

Answer 1

It means that the value was not changed. It was probably not changed because the column was already equal to the md5 hash of pass.