Question

delimiter $$

CREATE TABLE `tbl_locate` (
  `ID` int(11) NOT NULL AUTO_INCREMENT,
  `Locating` bit(1) DEFAULT NULL,
  `MainPower` bit(1) DEFAULT NULL,
  `Acc` bit(1) DEFAULT NULL,
  `PowerOff` bit(1) DEFAULT NULL,
  `Alarm` int(11) DEFAULT NULL,
  `Speed` int(11) DEFAULT NULL,
  `Direction` int(11) DEFAULT NULL,
  `Latitude` double DEFAULT NULL,
  `Longitude` double DEFAULT NULL,
  `DateTime` datetime DEFAULT NULL,
  `MainID` int(11) DEFAULT NULL,
  `IOState` int(11) DEFAULT NULL,
  `OilState` int(11) DEFAULT NULL,
  PRIMARY KEY (`ID`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=latin1$$

SQL STRING

SELECT * FROM tbl_locate WHERE DateTime=(SELECT MAX(`DateTime`) FROM tbl_locate WHERE MainID=1,2,3)

我想返回主id为1或2或3的最新行数据，
所以，需要返回3行最新日期时间第1行是id 1最新日期时间
第二行是id 2最新日期时间
第三行是id 3最新日期时间

怎么做？

Answer 1

SELECT        *
FROM          tbl_locate AS a
INNER JOIN     
(
    SELECT    MainID, Max(DateTime) AS DateTime
    FROM      tbl_locate
    GROUP BY  MainID
) AS b
ON            a.MainID = b.MainID
AND           a.DateTime = b.DateTime
WHERE b.MainID in(1,2,3)

试试这个

Answer 2

按DateTime订购，并获得前3行：
SELECT * FROM tbl_locate ORDER BY DateTime LIMIT 3

Answer 3

这应该有效：

SELECT * 
FROM tbl_locate t
  JOIN (SELECT Max(DateTime) MaxDateTime, MainId
        FROM tbl_Locate
        WHERE MainId IN (1,2,3)
        GROUP BY MainId) t2 
   ON t.MainId = t2.MainId AND t.DateTime = t2.MaxDateTime

这应该返回3行，Main ID 1,2,3各一行及其对应的Max（DateTime）。但是，如果存在多个具有相同DateTime的行，则它将返回多个记录。

以下是小提琴示例：http://sqlfiddle.com/#!2/f2c49/1

如果存在多个具有相同日期的记录，您需要引入一个RANK以确保您只为每个MainId返回一条记录：

SELECT *
FROM (
SELECT 
   @rowNumber:= IF(@prevRow=t.MainId, @rowNumber:=@rowNumber+1, 1) rank,
  t.* , 
  @prevRow:=t.MainId
FROM tbl_locate t
  JOIN (SELECT 
        Max(DateTime) MaxDateTime, MainId
        FROM tbl_Locate
        WHERE MainId IN (1,2,3)
        GROUP BY MainId) t2 
   ON t.MainId = t2.MainId AND t.DateTime = t2.MaxDateTime
JOIN (SELECT @rowNumber:= 0) t3

 ) t
WHERE rank = 1;

http://sqlfiddle.com/#!2/dce87/2

Answer 4

试试这个：

SELECT
    T1.*
FROM tbl_locate T1
    LEFT JOIN tbl_locate T2
        ON T1.MainID = T2.MainID
          AND T1.`DateTime` < T2.`DateTime` 
WHERE T2.Id IS NULL
  AND MainID IN (1,2,3)

返回的数据是Max Datetime和不同的标识不同的行--MYSQL

SQL STRING

4 个答案: