Solution to URL value passing callback

Callback php + js & nbsp for URL-based value passing. in the unsubmitted status, select a value in the drop-down box and execute database query on the value passing through jsURL to the new PHP page, then, return the query result to the original page so that php on the original page can use the returned value as the query condition when executing a new query.
Php + js
In the unsubmitted status, select a value from the drop-down list. on the new PHP page that passes the value through the js URL, execute the database query and return the query result to the original page, how can I use php on the original page to execute a new query and regard the returned value as a query condition?


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Ajax