MySQL：从匹配id的其他表中获取多个数据

Question

I have two table one is battle and second is user the table structure and records in the tables are like below The user_id and competitor_id are the ids from user table

A. Battle table

   battle_id | user_id | competitor_id 
        1     | 1       |  5      
        2     | 3       |  4
        3     | 2       |  3

B.   User table

      ID | user_name 
      1  | ABC
      2  | XYZ
      3  | PQR
      4  | MNO
      5  | UVW

I want to fetch the name user_id and competitor_id The Output Should look like below

Output

   battle_id | user_id | competitor_id | user_name |  competitor_name
        1     | 1       |  5           | ABC       | UVW
        2     | 3       |  4           | PQR       | MNO
        3     | 2       |  3           | XYZ       | PQR

Answer 1

Try this:

SELECT `Battle`.`battle_id`,`Battle`.`user_id`,`Battle`.`competitor_id`,`User`.`user_name`,(SELECT `User`.`user_name` FROM `User` WHERE `Battle`.`competitor_id` = `User`.`ID`) AS `competitor_name` 
FROM `User` JOIN `Battle` ON (`Battle`.`user_id` = `User`.`ID`) 
ORDER BY `Battle`.`battle_id`

Answer 2

Two joins will do:

SELECT b.battle_id, b.user_id, b.competitor_id, u1.user_name AS 'user_name', u2.user_name AS 'competitor_name'
FROM `Battle` AS b
JOIN `User` AS u1 ON u1.ID = b.user_id
JOIN `User` AS u2 ON u2.ID = b.competitor_id