php - duplicate entry

Question

what should do if the entry are doubled?

<?php
require_once('auth.php');
session_start();
$exam = $_SESSION['exam'];
$subject_id = $_SESSION['exam']; 
$_SESSION['sub'] = $subject_id; 
$subject_title = $_POST['subject_title'];
$subject_description = $_POST['subject_description'];
$con = mysql_connect("localhost","root","");
if (!$con)
{
die('Could not connect: ' . mysql_error());
}  
mysql_select_db('db_compre', $con);
$sql = "INSERT INTO examsubjectrecord_table(subject_id , subject_title ,
        subject_description)
        VALUES ('$subject_id','$subject_title', '$subject_description')";

if (!mysql_query($sql,$con))
{
die('Error: ' . mysql_error());
}
else
{
header("location: addsubject.php?exam=".$exam ."");
}
?>`  

Notice: A session had already been started - ignoring session_start() in C:\xampp\htdocs\compre\admin\addsubjectacc.php on line 4  
**Error: Duplicate entry '1' for key 'PRIMARY'**

Olegas · Accepted Answer · 2012-01-21 16:09:17Z

3

It depends on yout application business-logic.

You can notify a user about a duplicated entry or silently update information with INSERT ... ON DUPLICATE KEY UPDATE ... SQL statement.

answered Jan 21, 2012 at 16:09

Olegas

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Comments

pmr · Accepted Answer · 2012-01-21 21:46:28Z

1

In your database you have a primary key of subject_id which cant have duplicates.

If you need to have duplicates in the subject_id column then you should add a column and set it as a primary key in your database. For example add another column unique_id and set it to auto_increment and as a primary key for row identification.

edited Jan 21, 2012 at 21:46

pmr

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answered Jan 21, 2012 at 16:11

Kypros

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Comments

Oldskool · Accepted Answer · 2012-01-21 16:09:18Z

0

Basically, you'll first want to check if the value you're trying to insert into your primary key field already exists.

So if you primary key field is subject_id, you'd need to check if that already exists by doing a select query followed by PHP's mysql_num_rows function. For example:

$subject_id = 1337;
$check = mysql_query("SELECT `subject_id` FROM `examsubjectrecord_table` WHERE `subject_id`=" . $subject_id);

// See if anything was returned
if(mysql_num_rows($check) > 0) {
    // We have something with this subject_id already!
    echo "Cannot insert duplicate subject!";
} else {
    // All clear, run your INSERT query here
}

answered Jan 21, 2012 at 16:09

Oldskool

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6 Comments

Oldskool Over a year ago

@MichaelMior If you want to deliver half work and don't build in any checks and have ERRORS returned, well then yes ... I guess you could omit this step. If you want to build a proper application though, you'd better try to prevent errors from actually happening.

Michael Mior Over a year ago

There's nothing wrong with an error when it's expected as long as it's handled properly. Especially if the common case is no errors. You're just adding unnecessary overhead and complexity.

Oldskool Over a year ago

@MichaelMior That's pretty much exactly my point, the error needs to be handled properly. Not checking for duplicate keys before inserting one is not handling it.

Michael Mior Over a year ago

What is the downside of allowing the database to give you an error message? You can check for the error and handle it at that point instead of writing logic to check the error yourself.

Oldskool Over a year ago

@MichaelMior The downside is that mysql_query doesn't allow you to actually catch the cause of the error. It just returns false, which can have tons of reasons. It would be another story if OP was using PDO, which would throw a PDOException, but that's not the case here.

|

Community · Accepted Answer · 2023-11-17 19:22:09Z

0

Which column is your primary key? I'm going to assume that's subject_id. This needs to be unique for each row in your table. The easiest way to ensure this is to use AUTO_INCREMENT and then avoid inserting the subject_id at all. It will be assigned automatically.

If you need to find out what the ID of new subjects is, you can use mysql_insert_id.

edited Nov 17, 2023 at 19:22

CommunityBot

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answered Jan 21, 2012 at 16:09

Michael Mior

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