Question

This is kind of similar to this question:

PHP MySQL INSERT fails due to unique constraint

but I have a different twist. Let’s say I have a table with only one column. The column’s name is “title” and it has a unique constraint placed on it.

First I insert a row where title = “something”. The next time I try to insert “something” it will fail due to a unique key constraint (which is good). What I’d like to do is allow it to fail, and check the error code provided by mysql to ensure it failed due to a unique key constraint. (i.e. let the database handle the uniqueness, and I just handle the error code and tell the user that title already exists when the result comes back).

Is there a way to do this?

Answer 1

http://dev.mysql.com/doc/refman/5.5/en/error-messages-server.html

http://php.net/manual/en/function.mysql-errno.php

I’ve had to do this in the past, and it’s not fun:

if( mysql_errno() == 1062) {
    // Duplicate key
} else {
    // ZOMGFAILURE
}

A note on programming style (Credits to jensgram from this answer)
You should always seek to avoid the use of magic numbers. Instead, you could assign the known error code (1062) to a constant (e.g. MYSQL_CODE_DUPLICATE_KEY). This will make your code easier to maintain as the condition in the if statement is still readable in a few months when the meaning of 1062 has faded from memory 🙂