preventing duplicate row insertion in php/mysql

Question

how do you prevent the entry of duplicate records in php mysql? validating input before insertion to the table.

i am currently building a user registration section f

Answer 1

Define unique constraints for the username and email columns:

ALTER TABLE your_table ADD CONSTRAINT uk_username UNIQUE (username)
ALTER TABLE your_table ADD CONSTRAINT uk_email UNIQUE (email)

If the value attempting to be insertered or updated already exists in the table, MySQL will return an error stating the query violates the appropriate unique constraint (possibly both). It's up to you to setup PHP to handle this gracefully.