PHP/MySQL - Check for duplicate rows

[EpidemiK]

Basically I have a user signup/login system on a MySQL backend. However, visitors can sign up multiple times with the same username. How would I get MySQL to check if there already exists the username in the database?

The table is like this

id username password email
1 blahblahb blahblah blah@blah.com

[kabatak]

If your using phpMyAdmin you can simply click the "unique" button under the actions.
You can also run this query



ALTER TABLE `your_tbl` ADD UNIQUE (`your_username`)


just change "your_" to the actual names.

[kabatak]

by the way, that will cause mysql to return an error msg when you try to insert an existing value. so it is a good practice to check if the field exist first in your php script before you do the actual insert.

[EpidemiK]

Thanks for your help, but I just found out how. All I did was do

SELECT username FROM users WHERE username='$blah'
and count the number of rows. If it was >= 1, then it would return an error, else it would process it.

[kabatak]

yeah. however my 1st post is a good backup like if somebody tried to hack the script, they still cant push thru coz mysql will block it.

[EpidemiK]

Somenoe just tried to use SQL injection tactics on my site, and I just want to say thanks because you reminded me to fix it up. :)