Managing & Using MySQL, 2nd Edition

Handling MySQL Errors

The script in Example 11-2 includes MySQL error handling. Errors can occur in many different cases. For example, the MySQL DBMS might be unavailable, it might not be possible to establish a connection because the DBMS user’s credentials are incorrect, or an SQL query might be incorrectly formed.

Consider a fragment from Example 11-2:

// Run the query
if (!($result = @ mysql_query ($query, $connection))) 
   showerror(  );

If the mysql_query( ) function returns false, the function showerror( ) is called to output details of the error:

// Show an error and stop the script
function showerror(  )
{
   if (mysql_error(  ))
      die("Error " . mysql_errno() . " : " . mysql_error(  ));
   else
      die("Could not connect to the DBMS");
}

If a MySQL error has occurred, the script outputs the error number and a descriptive string, and the PHP engine stops. If the error isn’t a MySQL error, there is a problem connecting to the DBMS with mysql_pconnect( ). The showerror( ) function is part of the db.inc include file.

When a function such as showerror( ) is used, MySQL function calls are usually prefixed with the @ operator. The @ stops the PHP engine from outputting its own internal error messages. If the @ is omitted, the output of showerror( ) is shown interleaved with the PHP engine’s internal error messages, which can be confusing to debug.