我正在学习SQL并希望通过id和userid组合3个表,6个输出(每个表2个)。这一切看起来都是正确的但是给了我这个错误:#1054 - 'on clause'中的未知列'guestbook.id'。
SELECT yacka.userid, yacka.yackmane, registered.id, registered.Name, guestbook.id, guestbook.name FROM yacka
LEFT JOIN registered on yacka.userid = guestbook.id
LEFT JOIN guestbook on yacka.userid = guestbook.id;
答案 0 :(得分:0)
LEFT JOIN已注册应该已开启条件已注册表,但您使用的是留言簿表格仍然没有声明,将查询更改为下面一次不会抛出异常
SELECT yacka.userid, yacka.yackmane, registered.id,
registered.Name,guestbook.id, guestbook.name FROM yacka
LEFT JOIN registered on yacka.userid = registered.id
LEFT JOIN guestbook on yacka.userid = guestbook.id;