SELECT returing null always

I have small database(MySQL) with table called user_information. The columns which the table has are: uid, firstname, lastname,age,gender and mail. I want to get all information about user with ID.So the query will be:

SELECT * FROM user_information WHERE uid = 0;

There is row where uid=0 but I get null on every column(the date isn't null). If I try to get row for example with given first name I don't have any problems.

SELEC * FROM user_information WHERE firstname = "test";

This query will work prefect. The uid column is primary key. Any idea why I face this problem any help is appriciated?