如何將一列連接到另一個表中的所有列

Question

我有兩張桌子，球員和陣容表與團隊中的所有球員

陣容表有這個列

 `match_id`, `goalkeeper`, `center_back`, `center_back_2`, `right_outside_back`, `left_outside_back`, `defensive_center_midfielder`, `center_midfielder`, `attacking_center_midfielder`, `right_winger`, `left_winger`, `center_forward`

並且所有列都具有玩家表中一名玩家的 ID

如何將這里的所有列加入到玩家表中？

Answer 1

與此相符的東西：

select match_id, 
gk.player_name as goalkeeper, 
c_back.player_name as center_back 
from matches
left join players as gk on gk.id = matches.goalkeeper
left join players as c_back on c_back.id = matches.center_back
...
where match_id = x

基本上很多left_joins。

如果您重新設計數據庫模型並添加包含以下列的表：match_id、position_id、player_id 事情會簡單得多，數據庫引擎將感謝您。

那么你的 SQL 看起來會簡單得多：

select positions.* from position_definition as positions
left join (select mp.*, players.player_name from  match_players as mp left join players on mp.player_id = players.id where match_id = x) 
as team on team.position_id = positions.id

（類似的東西，這里沒有檢查准確性）還添加了一個額外的表格，其中包含一場比賽中所有位置的列表。