Capture mysql database error and use it in php

I created the following table for user to user subscriptions.

CREATE TABLE IF NOT EXISTS `subscriptions` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `user_id` int(11) NOT NULL,
  `subscribed_to` int(11) NOT NULL,
  `date` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`),
  UNIQUE KEY `unique_subscription` (开发者_如何学JAVA`user_id`,`subscribed_to`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=76 ;

I'm disallowing identical rows by making the columns user_id and subscribed_to unique. If a user tries to resubmit the same data I get:

A Database Error Occurred Error Number: 1062

Duplicate entry '62-88' for key 'unique_subscription'

INSERT INTO subscriptions (user_id, subscribed_to, date) VALUES ('62', '88', '2011-07-11 19:15:13')

Line Number: 330

I'm preventing the database error by checking if an identical row exists before trying to insert data.

$query = "SELECT COUNT(*) FROM subscriptions WHERE (user_id = '62' AND subscribed_to = '88')";

if ($query > 0)
{
    //display already subscribed message
}
else
{
    //insert new row
}

The database already checks the table and returns an error. The select count(*) query above seems redundant. Do I really need to check the table once more in my application? Is there a way to capture the database error if it occurs, and do something with that in my application?

If you have an idea how please share an example. I haven't a clue how this is done..!

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Check out PHP function mysql_error

You can wrap the db call within a try catch statement for functions that throw exceptions to prevent your application from crashing.

PHP function mysql_query does not throw exception on error, but returns FALSE. You can check the return value and execute mysql_error to find out the trouble or log it.