How to check if a value already exists to avoid duplicates?

Question

I\'ve got a table of URLs and I don\'t want any duplicate URLs. How do I check to see if a given URL is already in the table using PHP/MySQL?

Answer 1

To guarantee uniqueness you need to add a unique constraint. Assuming your table name is "urls" and the column name is "url", you can add the unique constraint with this alter table command:

alter table urls add constraint unique_url unique (url);

The alter table will probably fail (who really knows with MySQL) if you've already got duplicate urls in your table already.