How can I get the ID value of the previous page in PHP?

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How to get the ID of the first page on the second page

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The code has been written very clearly, just to the first page of the php file output $freebuy_item[' ID ' to the first page on the line, jump to the second page of the URL is this format checkin.php?id=123, you in the second page corresponding PHP with $ _get[' id ') gets the

URL Delivery
Don't you have id= "+id?"
$_get[' ID '] not taken?

Why do you have to add a # before?

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