Question

我有一个包含主行的表，我想要所有这些行。然后有2个表可能没有匹配的行，但如果这些表没有匹配的行，我仍然希望主表中的行。

此查询有效，但如果所有3个表中都没有行，则不会返回任何内容。我在php中使用mysql。

SELECT PS_Info.* , PS_Guides.Guide, PS_User.UserID FROM PS_Info 
JOIN PS_Guides ON PS_Info.ID = PS_Guides.InfoID 
JOIN PS_User ON PS_Info.ID = PS_User.InfoID 
WHERE PS_Info.GameID = :ID AND PS_User.UserID = :UserID

我正在尝试显示PS_Info中的列表。然后我想隐藏其中一些项目，如果用户将它们设置为隐藏（PS_User = UserID，InfoID）。如果PS_User中没有任何内容，则他们没有将此项设置为隐藏，因此我想显示它。 PS_Guides包含有关列表中每个项目的额外信息。并非所有项目都包含额外信息，因此如果此表中没有行，则我不显示它。

Answer 1

您正在寻找＆＃39; left join＆＃39;。

SELECT PS_Info.* , PS_Guides.Guide, PS_User.UserID   FROM PS_Info 
LEFT JOIN PS_Guides ON PS_Info.ID = PS_Guides.InfoID 
LEFT JOIN PS_User ON PS_Info.ID = PS_User.InfoID 
WHERE PS_Info.GameID = :ID AND PS_User.UserID = :UserID

Answer 2

SELECT PS_Info.* , PS_Guides.Guide, PS_User.UserID FROM PS_Info 
left JOIN PS_Guides ON PS_Info.ID = PS_Guides.InfoID //use left join 
left JOIN PS_User ON PS_Info.ID = PS_User.InfoID   //use left join 
WHERE PS_Info.GameID = :ID AND PS_User.UserID = :UserID

SQL三重连接表中的某些行可能不存在

2 个答案: