使用可能的空记录查询 SQL 值

Question

I have 4 tables that I want to run a single query on. I want specific values from each table that all relate to a single user.

However, some of these tables may not have any associated records. If there are no records in a given table, the query set comes back as empty (because there are no records pertaining to the specified user in the table).

Question

How do we pull all values for a user and insert blanks/null in the columns that have no values?

My query:

SELECT PLAYER.UUID,
       XP,
       RANKS.RANKNAME,
       HORSE.HEALTH_LEVEL,
       HORSE.SPEED_LEVEL,
       HORSE.JUMP_LEVEL,
       special_weapons.name
FROM PLAYER,
     HORSE,
     RANKS,
     Special_weapons
WHERE PLAYER.UUID = HORSE.UUID
  AND PLAYER.RANKID = RANKS.RANKID
  AND PLAYER.UUID = 'sldjnofw-adfdafd-113rsada'
  AND Player.uuid = special_weapons.uuid;

My table structure:

My table contents:

The special weapons table in this case is empty. Blanks should populate missing columns in the above query. Instead, an empty set is returned.

Answer 1

You need LEFT JOIN in such cases. Try below

SELECT player.uuid
      ,xp
      ,ranks.rankname
      ,horse.health_level
      ,horse.speed_level
      ,horse.jump_level
      ,special_weapons.name
FROM   player
LEFT   JOIN horse
ON     player.uuid = horse.uuid
LEFT   JOIN ranks
ON     player.rankid = ranks.rankid
LEFT   JOIN special_weapons
ON     player.uuid = special_weapons.uuid
WHERE  player.uuid = 'sldjnofw-adfdafd-113rsada';