Question

I have got a Mysql (5.1.58-1ubuntu1) ‘users’ table (InnoDB storage engine, utf8 general ci collation) with 3 fields (for simplicity) :

• id : int (primary key)
• username : varchar(255) – utf8_general_ci
• password : varchar(255) – utf8_general_ci

In this table there are only two records (always for simplicity):

id| username | password
-----------------------
1 | myuser   | custom1
2 | myuser2  | custom2

So, if i run this query

 select * from users where username = 0 and password = 0

mysql return me all records.

On the contrary , if i run the query below

select * from users where username = '0' and password = '0'

MySql return me an empty set.

For my opinion this behavior is very strange and it seems a Hard Bug.

Someone has any explanations?

Answer 1

It’s not a bug. You can only compare values of the same types, so MySQL silently converts your text ‘myuser’ to an integer with the value of 0.