Find Records from Different Tables [closed]

问题:

Requirement

Find and display all pilots (employee ID and name) who implemented flights on the planes of 'Commuter' type and ‘Normal’ type.

1st image is Plane_new table
2nd image is FlightI_new table
3rd image is Employee_new table

Solution

SELECT flightI_new.eid, employee_new.ename
FROM flightI_new
INNER JOIN employee_new ON flightI_new.eid = employee_new.eid
INNER JOIN plane_new ON flightI_new.pnum = plane_new.pnum
WHERE plane_new.ptype = 'Commuter' AND plane_new.ptype = 'Normal';

The code works with OR, but for some reason with AND i get "no rows returned".

Any idea how to solve it?

回答1:

Your AND does not work because records cannot have both ptype on the same record. But you should be able to use something like this:

SELECT flightI_new.eid, employee_new.ename
FROM flightI_new
INNER JOIN employee_new 
    ON flightI_new.eid = employee_new.eid
INNER JOIN plane_new 
    ON flightI_new.pnum = plane_new.pnum
WHERE plane_new.ptype IN ('Commuter', 'Normal')
GROUP BY flightI_new.eid, employee_new.ename
HAVING count(distinct plane_new.ptype) = 2;

See SQL Fiddle with Demo

Of you can use something like this:

SELECT distinct flightI_new."eid", employee_new."name"
FROM flightI_new
INNER JOIN employee_new 
    ON flightI_new."eid" = employee_new."eid"
INNER JOIN plane_new 
    ON flightI_new."pnum" = plane_new."pnum"
WHERE plane_new."ptype" = 'commuter'
  AND flightI_new."eid" IN (select flightI_new."eid"
                            FROM flightI_new
                            INNER JOIN employee_new 
                                ON flightI_new."eid" = employee_new."eid"
                            INNER JOIN plane_new 
                                ON flightI_new."pnum" = plane_new."pnum"
                            WHERE plane_new."ptype" = 'normal')

See SQL Fiddle with Demo

回答2:

the wrong is here

      WHERE plane_new.ptype = 'Commuter' AND plane_new.ptype = 'Normal';

plane_new.ptype cant have two things ,computer and normal in your database, it must be one of them thats why u get no rows returned. so maybe you mean something else. here in your WHERE statment u can use only OR. and they the rows returned are those who have computer and normal