Already existed data query and bypassing new entry in php mysql - php

Question

I have written a long program. Im just sharing here some lines to understand a concept which is my issue here. I want to check if the previous data is equal to the newly entered, if it is, then an error should occur that the data is already entered, without storing again in db. Following code is running but it duplicates data. It is not quite good. may you please check where I am wrong. thanks
Database Name Booking:
Table Name data:
Name: John, Anjel, Smith, David
CNIC: 33, 46, 33, 91
//// storing data in database from html form fields
<?php
$emp_name = addslashes($_POST['emp_name']);
$emp_cnic = addslashes($_POST['emp_cnic']);
?>
//// Selecting CNIC that is duplicated (already existed) on a new form submission
$already = mysql_query("SELECT CNIC FROM data WHERE CNIC = '$emp_cnic'");
//Dieing script without storing the data if it already exists.
if($already){
die('Sorry! you are already registered. For any query, contact the administrator. ');

Answer 1

You couls also REPLACE mysql function.
If not, just change your request with a COUNT() and check if the returned result is greater than 0.
I would also highly recommand you to go on PDO instead of still using mysql_* (which is deprecated / removed)

Answer 2

You could use mysql_num_rows
$already = mysql_query("SELECT CNIC FROM data WHERE CNIC = '$emp_cnic'");
$record_count = mysql_num_rows($already );
// $record_count > 0 means data already exist
if( $record_count > 0 ) {
// Show error
} else {
// Save data
}

Answer 3

The problem I see with your code is the following:
For SELECT, SHOW, DESCRIBE, EXPLAIN and other statements returning
resultset, mysql_query() returns a resource on success, or FALSE on
error.
For other type of SQL statements, INSERT, UPDATE, DELETE, DROP, etc,
mysql_query() returns TRUE on success or FALSE on error.
The error you mentioned when you use mysql_num_rows() is caused because of the false return of the unsuccessful query.
You are checking a value that might be not boolean, to solve this use:
if(!isset($already) OR mysql_num_rows($already) == 0){
// die
}
else{
// do stuff
}
This check if the query was unsuccessful or if it is empty, so you always get a boolean to check your result set.
As #Sakuto pointed out is important to use not deprecated functions, therefor instead of using mysql_query() you should use mysqli or PDO functions.For further information read this.