SQL查询 - 关系表上的双重条件

Question

我正在努力让所有使用英语和法语的用户根据上面的架构。我怎样才能做到这一点？

我尝试过类似的事情：

SELECT * FROM User
INNER JOIN UserLanguage on User.idUser = UserLanguage.idUser
INNER JOIN Language on UserLanguage.idLanguage = Language.idLanguage
WHERE Language.name = "FR" AND Language.name = "EN"

Answer 1

我正在使用子查询来计算每个用户说出的语言数量（FR或EN）。然后它返回所有使用这两种语言的用户的所有id。外部查询返回每个用户的所有列：

SELECT Users.*
FROM Users
WHERE idUser IN (
  SELECT UserLanguage.idUser
  FROM
    UserLanguage INNER JOIN Language
    ON UserLanguage.idLanguage = Language.idLanguage
  WHERE
    Language.name IN ("FR", "EN")
  GROUP BY
    UserLanguage.idUser
  HAVING
    COUNT(DISTINCT Language.name)=2
)

Answer 2

从

更改条件

WHERE Language.name = "FR" AND Language.name = "EN"

到

WHERE (Language.name = "FR" OR Language.name = "EN")

你不应该在数据库中有一个条目，它对一个字段有两个值，但如果你使用＆＃34; OR＆＃34;运算符，如果任一值相等，则应选择该条目。

Answer 3

SELECT * 
FROM User
WHERE 2 = (SELECT COUNT(*)
            FROM UserLanguage 
            INNER JOIN Language
              ON UserLanguage.idLanguage = Language.idLanguage
                 AND (Language.name = 'FR' OR Language.name = 'EN')
            WHERE User.idUser = UserLanguage.idUser)

Answer 4

总是尝试从圆圈的“中心”的角度来看待连接。在这种情况下，您尝试通过UserLanguage将“用户”加入“语言”，因此您的FROM表必须是“UserLanguage”。

所以基本上你在看：

SELECT * FROM UserLanguage
INNER JOIN User ON Userlanguage.idUser = User.idUser
INNER JOIN Language on Userlanguage.idLanguage = Language.idLanguage
WHERE (Language.Name = 'EN' OR Language.Name = 'FR');

Answer 5

 SELECT * FROM User
    INNER JOIN UserLanguage on User.idUser = UserLanguage.idUser
    INNER JOIN Language on UserLanguage.idLanguage = Language.idLanguage
 WHERE Language.name = "FR" AND Language.name = "EN"

您只需要更改

即可

 WHERE Language.name = "FR" AND Language.name = "EN"

到

 WHERE (Language.name = "FR" OR Language.name = "EN")

Answer 6

SELECT *
FROM Users u INNER JOIN UserLanguage ul
ON u.idUser = ul.idUser JOIN Language l
ON ul.idLanguage = l.idLanguage
WHERE l.LanguageName IN ('EN', 'FR')
ORDER BY u.idUser

Answer 7

您必须将UserLanguage表连接到自身，例如：

SELECT T1.idUser 
FROM UserLanguage AS T1
INNER JOIN UserLanguage AS T2
ON T1.idUser=T2.idUser
WHERE T1.idLanguage='EN'
AND T2.idLanguage='FR'