Question

我有两种类型的用户，我将它们保存在两个不同的表中，我需要根据类型选择此用户的数据，这是我的查询：

SELECT user_data_bis.name, user_data_bis.surname, 
       user_data_bis.avatarimage, user.externalid, user.type // User's Data
FROM user_wall_likes 
INNER JOIN user
    ON user.internalid = user_wall_likes.owner
INNER JOIN  (CASE user.type
                  WHEN user.type=0
                  THEN
                      (
                      SELECT name, owner, surname, avatarimage
                      FROM user_data
                      ) user_data_bis
                  WHEN user.type=1
                  THEN
                      (
                      SELECT name, "" AS surname, owner, icon AS avatarimage
                      FROM university_data
                      WHERE isdelete=0
                      ) user_data_bis
             END)
             ON user_data_bis.owner = user.internalid 
             WHERE user_wall_likes.wallid="619fd58836c9a826b9eafb4b4e81da24" 
                   AND user_wall_likes.isdeleted=0
             LIMIT 5

注意：当它说user_wall_likes.wallid="619fd58836c9a826b9eafb4b4e81da24时，此varchar是我的数据库中一列的示例

但是当我执行此查询时，它会显示我：

＃1064 - 您的SQL语法出错;检查与您的MySQL服务器版本相对应的手册，以便在＆＃39; CASE user.type WHEN user.type = 0＆＃39;附近使用正确的语法。在第6行

是否有一些方法可以根据这种情况user.type中的变量从表中提取数据？

Answer 1

您可以使用两个left join和coalesce()：

完成此操作

SELECT coalesce(ud.name, unv.name) as name,
       coalesce(ud.surname, unv.surname) as surname,
       coalesce(ud.avatarimage, unv.avatarimage) as avatarimage,
       u.externalid, u.type    -- User's Data
FROM user_wall_likes uld INNER JOIN
     user u
     ON u.internalid = uwl.owner LEFT JOIN
     user_data ud
     ON u.type = 0 AND ud.owner = u.internalid LEFT JOIN
     university_data unv
     ON u.type = 1 AND unv.owner = u.internalid
WHERE uwl.wallid = '619fd58836c9a826b9eafb4b4e81da24' AND uwl.isdeleted = 0
LIMIT 5;

请注意，您通常会ORDER BY LIMIT。

我可以在MySQL中将条件放入INNER JOIN吗？

1 个答案: