PHP - detect mysql update/insertion failure due to violated unique constraint

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

Answer 1

Why not just do a select first to see if the entry already exists. Or suppress an error altogether by using INSERT ON DUPLCATE KEY UPDATE, or even use the mysql IGNORE keyword. Why purposely cause an error?