Post request uses $_SERVER['QUERY_STRING'] to get the parameters of the url. Why only the first one is obtained?

Question

For example, when submitting a request for /xx/post/1?a='a'&b='b', use $_SERVER['QUERY_STRING'] to get the parameter value as a='a', why not a='a'&b ='b'

Answer 1

Just pass the string and do a little processing to make it more convenient to use