When connecting to MySQL, or executing a query, proper error handling is required. Many take this very seriously, and do a construct like mysql_connect() or die() or the equivalent with mysql_query(). For web apps this generally makes error codes end up on the user page, you can easily see this by doing a Google search for some of the common error texts. Slightly improved apps are nicer to the user and log the error separately.

But both approaches fail, fundamentally, as they don't take into account that not all errors are the same and, most importantly, many error are not fatal but require other forms of action. So let's look at that, look at what causes the errors so you truly understand that it's not fatal stuff, and how you can handle them.

When you get a "not successful" response back from a MySQL API function, you first need find out what the error is with mysql_errno() (and …