如何 select 连接表中的两行

Question

So i have two tables with information below one which is a holiday table which marks the location to and from and etc. and another table that has the information on the locations

holiday_id	location_from	location_to	start_time	end_time
1	21	43	13:00	17:00

Location_id	location_name
21	sydney
43	gold coast

I'd like to have an sql query which will return the names of the location to and from but because location name is under one column im not sure how to do it. any help is appreciated

Answer 1

You can join with the table, twice, using an alias:

select location_1.location_name, location_2.location_name, other, columns
from holidays
join locations location_1 on holidays.location_from = location_1.location_id
join locations location_2 on holidays.location_to   = location_2.location_id

Answer 2

select a.location_name,b.location_name from table1 
left join table2 on table2.Location_id = table1.location_from
left join table2 on table2.Location_id = table1.location_to

Answer 3

Just need to join to the location table twice. Once for the location_from and again for the location_to:

SELECT
    h.holiday_id,
    h.location_from,
    locfrom.location_name,
    h.location_to,
    locto.locatin_name,
    h.start_time,
    h.end_time
FROM    Holidays h
INNER JOIN Locations AS locfrom
    ON locfrom.Location_id = h.location_from
INNER JOIN Locations locto
    ON locto.Location_id = h.location_to;