PHP - Learning MySQL - page 445

Handling errors using the older MySQL library
The default MySQL (as opposed to MySQLi) library has two similar error-handling
functions that you can use to check for problems. The function mysql_errno( ) returns
an error number for the most recent MySQL function that used the specified connec-
tion; if no error occurred, it returns 0. Similarly, the function mysql_error( ) returns a
string describing an error for the most recent MySQL function that used the specified
connection; if no error occurred, it returns the empty string "" . Note that neither works
for the mysql_connect( ) function; both need a working connection as a parameter to
interrogate the MySQL server about the error. The old MySQL function library doesn't
have any equivalents for the MySQLi functions mysqli_connect_error( ) and
mysqli_connect_errno( ) , so you need to check for a failed connection yourself, perhaps
by calling the die( ) function to print an error message and stop processing.
Let's look at an example. Suppose you have the following fragment that tries to use the
nonexistent vapor database:
// Connect to the MySQL server
if (!($connection = @ mysql_connect("localhost", "root",
" the_mysql_root_password ")))
die("Cannot connect");
if (!(@ mysql_select_db("vapor", $connection)))
die(mysql_error($connection) . " (" . mysql_errno($connection) . ")");
The final line of the fragment concatenates a string that describes the error using
mysql_error( ) and then includes in parentheses the error number using
mysql_errno( ) . When you run the fragment, you get the output:
Unknown database 'vapor' (1049)
As with the MySQLi library, you could write a simple function to handle MySQL errors:
// Custom error handler function
function showerror($connection)
{
die(mysql_error($connection) . " (" . mysql_errno($connection) . ")");
}
You could then call this function instead of the die( ) function and pass it the
$connection parameter:
// Connect to the MySQL server
if (!($connection = @ mysql_connect("localhost", "root",
" the_mysql_root_password ")))
die("Cannot connect");
if (!(@ mysql_select_db("vapor", $connection)))
showerror($connection);