MySQL-如何从3个表中获取数据？

Question

我需要一个查询，根据3个表从1个表中检索数据：

Table1

UID _ GID

1%-0

2/2-1

3-1

4/2

Table2

1/2

2/2-3

3/4

4/5

Table3

盖德·CID

1/2

2-2-2

3-3-3

4-1

现在我需要从table3检索数据，其中table1.GID=1、table2.UID=table1.UID和table3.CID=table2.CID

Answer 1

你可以用这个：

SELECT Table3.* FROM Table1 LEFT JOIN (Table2, Table3) 
ON (table1.GID=1 and table2.UID=table1.UID and table3.CID=table2.CID)

Answer 2

除非我做了一个错误

SELECT 
    t3.*
FROM
    t3
        LEFT JOIN
    t2 ON t3.cid = t2.cid
        LEFT JOIN
    t1 ON t2.uid = t1.uid
WHERE
    t1.gid = 1;

附表：

CREATE TABLE IF NOT EXISTS `t1` (
  `uid` int(11) NOT NULL AUTO_INCREMENT,
  `gid` int(11) NOT NULL,
  PRIMARY KEY (`uid`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=5 ;

INSERT INTO `t1` (`uid`, `gid`) VALUES
(1, 0),
(2, 1),
(3, 1),
(4, 2);

CREATE TABLE IF NOT EXISTS `t2` (
  `cid` int(11) NOT NULL AUTO_INCREMENT,
  `uid` int(11) NOT NULL,
  PRIMARY KEY (`cid`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=5 ;


INSERT INTO `t2` (`cid`, `uid`) VALUES
(1, 2),
(2, 3),
(3, 4),
(4, 5);

CREATE TABLE IF NOT EXISTS `t3` (
  `lid` int(11) NOT NULL AUTO_INCREMENT,
  `cid` int(11) NOT NULL,
  PRIMARY KEY (`lid`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=5 ;

INSERT INTO `t3` (`lid`, `cid`) VALUES
(1, 2),
(2, 2),
(3, 3),
(4, 1);

Answer 3

您可以使用此查询。

SELECT table3.* 
FROM table1 
JOIN table2 
JOIN table3 
WHERE table1.GID=1 
and table2.UID=table1.UID 
and table3.CID=table2.CID