How to automatically display data rows related to the upper-level after select is selected in the next-level select-php Tutorial

After the select statement is selected, the next-level select statement automatically displays the data rows related to the upper-level. ajax does not understand how to submit the first-level select option to PHP for processing.

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Reference: http://blog.chinaunix.net/uid-7254998-id-145002.html

The action in this example is empty. the newbie certainly does not know where the problem is...

Right. I copied all the examples to a php file but it was not successful. I want to fill in the form action on another processing page, I think the first drop-down list will change the option of the second list based on the selected value.

Using jq is simple.

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