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I was wondering what methods/preventions other programmers use to stop data being entered twice into a MySQL database when a user refreshes on the same page as a form? Obviouly it happens and I need a good way to stop this.
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Preventing Duplicates from Occurring in a Table. You can use a PRIMARY KEY or a UNIQUE Index on a table with the appropriate fields to stop duplicate records. Let us take an example – The following table contains no such index or primary key, so it would allow duplicate records for first_name and last_name.
1- Remove duplicate values using 'DISTINCT' key in mysql query, if it is present in table. 2- Check whether the value is present in table or not using PHP and Mysql before inserting data into the table. 3- We can also avoid duplicate values storing in mysql table while inserting by primary key.
I call this a golden rule of web programming:
Never ever respond with a body to a POST-request. Always do the work, and then respond with a Location: header to redirect to the updated page so that browser requests it with GET.
This way, refreshing will not do you any harm.
Also, regarding a discussion here in comments. To protect from double posting from, say, accidental doubleclicking the Submit button, store an md5() of your form in a text file, and compare the new form’s md5 to the stored one. If they are equal, you are having a double post.
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