Returns the id of the previous page.

Returns the id of the previous page, but returns FALSE,
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Is there a post value passed on your previous page, and the url is directed to the current php file?

Var_dump ($ _ POST );
Hope the answer is helpful to you.

I think it's strange that the page actually has an ID ??

Output false
It's your var_dump ($ result); is there no data to query?

This is the value of the previous page

There should be no other errors

Whether the $ resurt ['id'] output from the previous page has a value or whether the URL is correctly transmitted

Are you sure you want to $ _ POST [file_id]; instead of $ _ POST ['File _ id'];

#5. the file_id is the url variable.
You cannot use $ _ POST ['File _ id'] to obtain the value.
Use $ _ GET ['File _ id ']

$ Field = $ _ GET ['field'];

The hyper-connection is transmitted in GET mode and obtained using $ _ GET.

Thank you. I have fixed it.