MySQL在查询的1个结果行中选择更多数据

Question

I have a table - friends which has 2 columns, both are users table id 's.

I have a table - users which has id and username .

I need a query that will return username1 , username2 from the friends table, instead of id 's.

I tried joining both tables, but it returns 2 result rows instead of one, which is not what I want.

I tried looking into multi select queries, but I didn't find anything particularly useful, is it possible to do that?

Answer 1

Left join the users table twice, once for each user:

SELECT 
    u1.username username1, 
    u2.username username2
FROM friends f
LEFT JOIN users u1
    ON f.first_id = u1.id
LEFT JOIN users u2
    ON f.second_id = u2.id

Where first_id and second_id are the id columns in your friends table.

SQL Fiddle

Answer 2

You can do it with 2 inner joins:

SELECT
    User1.Name user1_name,
    User2.Name user2_name
FROM
    friends
    INNER JOIN users User1 ON friends.User1_ID = User1.ID
    INNER JOIN users User2 ON friends.User2_ID = User2.ID