Question

我有两张桌子：

CREATE TABLE folders (
ID BIGINT PRIMARY KEY AUTO_INCREMENT,
uid BIGINT NOT NULL,
driveid BIGINT NOT NULL,
foldername VARCHAR(64) NOT NULL,
icon_url varchar(260),
time_created timestamp NOT NULL default '0000-00-00 00:00:00',
time_updated timestamp NOT NULL default '0000-00-00 00:00:00' on update CURRENT_TIMESTAMP,
time_expires timestamp NOT NULL default '0000-00-00 00:00:00'
) ENGINE=MyISAM DEFAULT CHARSET=utf8;


CREATE TABLE drives (
ID BIGINT PRIMARY KEY AUTO_INCREMENT,
uid BIGINT NOT NULL,
drivename VARCHAR(100) NOT NULL,
icon_url varchar(260),
time_created timestamp NOT NULL default '0000-00-00 00:00:00',
time_updated timestamp NOT NULL default '0000-00-00 00:00:00' on update CURRENT_TIMESTAMP,
time_expires timestamp NOT NULL default '0000-00-00 00:00:00'

) ENGINE=MyISAM DEFAULT CHARSET=utf8;

我想选择驱动器和所有文件夹：

uid = UID NUMBER
在文件夹中，dbid = ID来自驱动器UID = given UID number

我想要一个查询并在单个响应中获得整个结果。可能吗？如果是这样请建议，我不想粘贴我尝试的东西，因为他们是愚蠢的，我尝试了内连接，左连接，混合查询，但我没有接近。

Answer 1

最终，这相当于LEFT JOIN有两个条件。如果uid在drives中没有关联文件夹的记录，则该驱动器将与文件夹列中的NULL一起返回。 driveid必须与drives.ID匹配，uid必须相同;这两个都将在ON子句中指定。

SELECT
  drives.ID AS driveid,
  drives.drivename,
  drives.uid,
  folders.ID AS folderid,
  folders.foldername,
  folders.icon_url,
  drives.time_created AS drive_time_created,
  drives.time_updated AS drive_time_updated,
  drives.time_expires AS drive_time_expires,
  folders.time_created AS folders_time_created,
  folders.time_updated AS folders_time_updated,
  folders.time_expires AS folders_time_expires
FROM
  drives
  LEFT JOIN folders
    ON drives.ID = folders.driveid
    AND drives.uid = folders.uid
WHERE
  drives.uid = [the-specified-uid]

Answer 2

我很确定您需要union查询。我不确定查询是什么，因为您的问题没有指定样本数据或所需结果。例如，不清楚您想要比较哪个用户ID。

但是，以下内容应该与您想要的非常接近：

select d.id as driveid, NULL as folderid
from drives d
where d.uid = @UID
union all
select d.id, f.id as folderid
from drives d join
     folders f
     on f.dbid = d.id
where f.uid = @UID;

单查询中的MySQL双查询

2 个答案: