mysql 使用内连接查询 2 个表

Question

我想加入 Table A 和 Table B 并显示每辆卡车的最新条目。

Table A列：TA ID，Truck_Num，Serial_Num
Table B 列：TB ID，Serial_Num，纬度，经度，日期时间

期望的输出

 Truck   |     DateTime     |    Serial_Num   |       Lat   |      Long                
   1     |     datestamp    |       123       |        1    |       -1                                     
   2     |     datestamp    |       456       |        2    |       -2

使用连接查询

SELECT a.Truck b.Lat b.Long b.DateTime FROM TB as b INNER JOIN TA AS a a.Serial_Num=b.Serial_Num;

我试过了，但它只给我最近的条目时间。

SELECT a.Truck b.Lat b.Long b.DateTime FROM TB as b INNER JOIN TA AS a a.Serial_Num=b.Serial_Num WHERE b.DateTime = (SELECT MAX(b.DateTime) FROM TB tb WHERE a.Truck_Num=Truck_Num);

Answer 1

这将显示每辆卡车的最新物品。如果您要显示的其余信息在所有行中都相同，那么您可以将其放在 group by 子句中，如果不是，则必须使用此结果进行连接

SELECT Serial_Num, MAX(DateTime) FROM TB GROUP BY Serial_Num;

如果数据不相等且您不能将其放在 group by 子句中，则这是您必须执行的连接

SELECT Truck_Num, Lat, Long, maxDateTime FROM TB as b 
   INNER JOIN TA AS a ON a.Serial_Num=b.Serial_Num
   INNER JOIN (SELECT Serial_Num, MAX(DateTime) as maxDateTime
               FROM TB GROUP BY Serial_Num) as c 
               ON b.Serial_Num=c.Serial_Num AND maxDateTime = DateTime

Answer 2

应该可以，你可以检查这个问题：

SELECT
    ta.Truck,
    tb.Lat,
    tb.Long,
    MAX(tb.DateTime),
    ta.Serial_Num as Serial_Num
FROM
    TB as tb
INNER JOIN
    TA as ta
ON (tb.Serial_Num = ta.Serial_Num)
GROUP BY
    tb.Serial_Num

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