How can I detect a duplicate post in PHP?

Question

I have a form which inserts the text (of an article) into a database. When a user submits an article (that has already been submitted) it gets submitted also into the db.

How can I detect a duplicate post (like on stackoverflow)?

Should I select everything from the database and check if the submitted post is like a one before. (I want to post the duplicate alert on the article page as the first comment)

Any help appreciated.

Thanks...

You could compare the contents of your database with the article and see if there are any similar records. But that will fail when there is a tiny difference (an extra or left-out character). — Jules, Aug 26 '11 at 11:38
The stackoverflow system consists of a (probably really complex) set of match algorithms. It's not easy to copy. If you really want to check for duplicate content, you should have a look at Full Text Search on MyISAM tables in MySQL. — Rijk, Aug 26 '11 at 11:54

score 2 · Accepted Answer · answered Aug 26 '11 at 11:37

2

Create an unique ID, e.g. with uniq_id(), put it in a hidden field within your HTML form, then save it in the database in a field that is set to UNIQUE. When the INSERT operation fails, you know that the POST has already been sent before.

answered Aug 26 '11 at 11:37

ty812

3,293
19
36

I love you solution mate. :) – kta Aug 06 '14 at 11:47

score 1 · Answer 2 · answered Aug 26 '11 at 12:59

1

If You will have hidden id, that you get from db when try to edit some content, You can use code like this:

if (isset($_POST['id']) && trim($_POST['id']) != '') {
    $query = 'UPDATE table_name
                    SET
                      `key` = \'' .$_POST['key']  . '\'
                    WHERE `id` = \'' . $_POST['id'] . '\'', 0;
  } else {
    $query = 'INSERT INTO table_name
                                  SET
                                `key` = \'' . $_POST['key'] . '\'', 0;
  }

answered Aug 26 '11 at 12:59

YamahaSY

289
3
17

In case anyone sees that and tries to use it, beware that as written it is **wide open to SQL Injection attacks**. If you do this for real, you should use query parameters rather than concatenating the user's input into the SQL. See [How can I prevent SQL injection in PHP?](https://stackoverflow.com/q/60174/157957) – IMSoP Jun 18 '22 at 14:24

How can I detect a duplicate post in PHP?

2 Answers2