MySQL查询两次连接同一张表，没有重复

Question

I have a table users

id, ip, opponent
1, 123.123.123, 2
2, 123.123.123, 1
3, 123.123.123, NULL

I need query that, show me list of versus ips without duplicates.

ip_first_opponent, ip_second_opponent

How can I do it, i am newbie in sql.

Answer 1

In case you want to get all the ips of the opponents of the user with id x, you can do the following:

SELECT DISTINCT(opponents.id) FROM users AS me, users AS opponents WHERE me.id=x and me.opponentId=opponents.id

(So you join the table users to itself with the constraint that the opponent id is the same as the id of the opponent and the DISTINCT only outputs different ips.)

Edit: Since you want to select the ip of the user and his opponents, the query becomes:

SELECT DISTINCT me.ip, opponents.ip FROM users AS me, users AS opponents WHERE me.opponentId=opponents.id