Mysql SELECT for Friends系统

Question

I have this table

conncections

id_user connectedto
    1       4
    2       4
    3       1
    1       5

i would like to do a SELECT that gives me back all the numbers that have a relation with the number 1 and the number 1 itself. Therefore 1 4 3 5 as result.

Answer 1

Something like

SELECT DISTINCT id_user as related
FROM connections
WHERE connectedto = 1
UNION
SELECT DISTINCT  connectedto as related
FROM connections
WHERE id_user = 1

With UNION duplicate are removed