I wished if these SQL were similar but I tried to use my SQL that I used to run in Oracle in MySQL but I get an error message. (I wanted the source_city to be from an input from the form so I called it s_city and dest city as $d_city.
I hear that MySQL doesnt use CONNECT BY... what else can I use?
Also Can I use a CASE in SELECT? (Thank you)

$a_query = "SELECT *
FROM (SELECT Flight_num, (CASE WHEN LEVEL=1 THEN Source_city
ELSE PRIOR Source_city END) AS S_City, Dest_city,
(CASE WHEN LEVEL=1 THEN (arr_time - dept_time)
WHEN LEVEL=2 THEN (arr_time - dept_time)+(PRIOR arr_time - PRIOR dept_time)
END) AS Tot_Time FROM Flight
START WITH source_city = $s_city
CONNECT BY PRIOR dest_city = Source_city AND Dest_city = $d_city) ALL_COR
WHERE Dest_city = $d_city";