Description:
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I have coded a page in php to add/edit/delete some values. The three actions are checked with the help of get variables.

The problem is when i submit the page once, the values are getting entered to the database twice. That is, two records are created with the same values.

I am using a header("location: ...") function to the same page with change in the query string. 

I have watched that the same location (as when adding) is retained and getting submitted even if i had coded for a change in location using header function.

The interesting thing is that this not happening always. Sometimes it works correctly. Many of my friends had the same issues and i was totally stuck with the problem.

Please help me out on this issue.

Reproduce code:
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Create a page which have the codes of insert, update, delete with actions distinguished by the querystring values like add=yes, update=yes, delete=yes

These values are checked like

if (isset($HTTP_GET_VARS["add"]) && $HTTP_GET_VARS["add"]=="yes")

When i click on the add button, i have written a javascript to submit the page, which will be like

pagename.php?add=yes

after the insert query is executed, the next statement is to call the same page with different querystring values. This will be like

header("location: pagename.php?id=newidcreated");
exit();

Expected result:
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Only a single entry is to be made to the table.

Actual result:
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Sometimes the data is submitted twice and two entries with the same details are getting posted to the table, which leads to duplicate values.