Not allowing duplicate entries in a field

[LanceT]

Lets say I have an script that inserts some stuff to a database and I want to check if there is a duplicate entry, and if so, prevent the user from adding the stuff (in this case, a username).

Any way to do this and using the least amount of system resources? The list that the code will be checking will be very long.

[artacus]

Well on the mysql side, you'll add a unique index on that field. That will prevent dups from being added. But most times you'll check if the record is there; if it is, update it; if not insert it.

[LanceT]

Well lets say we want to register and it's a username. Obviously we can't have duplicate usernames. So I want to display an error message if the username is taken.

I'm pretty sure this syntax won't work, but something like this.

[code]
if  ( $username exists ) {
echo "sorry, that username is taken";
}
[/code]

Some code would be helpful!

Thanks guys.

[fenway]

Well, like artacus said, if you have a unique index, you can simply attempt to add it, and catch the error.

[LanceT]

[quote author=fenway link=topic=124651.msg517276#msg517276 date=1170181761]
Well, like artacus said, if you have a unique index, you can simply attempt to add it, and catch the error.
[/quote]

How do i add the unique index?

[fenway]

Depends through what interface.. but ADD UNIQUE INDEX indexName ( columnName) will work too.