Question

我正在使用SQL Server，我有两个表

player：

    player  guildId
--------------------
    a       1
    b       2
    c       2
    d       2
    e       1
    f       1
    g       1

game：

    player  gameId
--------------------
    a       4
    b       1
    c       2
    d       1
    e       3
    f       2
    g       2

我想创建一个名为view_test的视图，

视图的结果：

select * from view_test where guildId = 2 and gameId = 2

显示

  player joined
----------------
    b    false
    c    true
    d    false


select * from view_test where guildId = 2 and gameId = 1

   player joined
-----------------
    b     true
    c     false
    d     true

select * from view_test where guildId = 2 and gameId = 3

  player joined
----------------
    b    false
    c    false
    d    false

select * from view_test where guildId = 1 and gameId = 4

  player joined
----------------
    a    true
    e    false
    f    false
    g    false

我该怎么做这个SQL？

由于

Answer 1

尝试这样

select id,case when count(*)=2 then 'true' else
'false' end from (
select id from player where guildId=2
union all 
select id from game where gameId=2
) as tt group by id

Answer 2

尝试此查询我的朋友：

with t as
(select t1.id,t1.guildId,t2.gameId  from player t1,game t2 where t1.id = t2.id)
select id,case when gameId = var.VarGameId then 'True'else 'False' end as Joined from t, 
(select 1 as VarGameId, 2 as VarGuildId)var where t.guildId = var.VarGuildId;

您可以在我的查询中使用var之类的内容来更改variables.

SQL Fiddle

Answer 3

您需要与所有游戏ID交叉加入玩家才能获得所有可能的组合。然后你在游戏桌上查看组合。所以基于以下观点：

select player.player, player.guildid, gameids.gameid,
  case when 
  (
    select count(*) 
    from game 
    where game.player = player.player 
    and game.gameid = gameids.gameid
  ) > 0 then 'true' else 'false' end as joined
from player
cross join (select distinct gameid from game) gameids;

声明

select * from view_test where guildId=2 and gameId=2

会导致

  player  guildId  gameid  joined
---------------------------------
    b     2        2       false
    c     2        2       true
    d     2        2       false

Answer 4

如果您需要检查一个公会（或有限数量）和一个游戏（或有限数量），那么您可以使用这样的查询：

SELECT p.player
  , (EXISTS (SELECT player FROM game WHERE player=p.player AND gameId=1)) AS joined
FROM player p
WHERE p.guildId=2

我不会创建一个视图......因为这需要所有玩家与所有不同游戏的完整笛卡尔联盟。我不能确定一旦你从该视图中选择，引擎就能够通过视图优化对基础表和索引的访问，并在合理的时间内给你结果。

视图可能是这样的：

SELECT p.player, p.guildId, g.gameId
  , (EXISTS (SELECT player FROM game WHERE player=p.player AND gameId=g.gameId)) AS joined
FROM player p JOIN (SELECT DISTINCT gameId FROM game) g

我必须添加...我不使用SQLServer ......我不确定它是否支持EXISTS子选择表达式。

SQL：从两个表中搜索

4 个答案:

SQL Fiddle