内部连接2个表的mysql查询

Question

我想连接表A和表B并显示每辆卡车的最新条目。

1. 表A列：TA ID，Truck_Num，SERIAL_NUM
2. 表B列：TB ID，SERIAL_NUM，纬度，经度，日期时间

希望的输出

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，但它只是给我最近的报名时间。

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

这将显示每辆卡车最近的项目。如果你想显示信息的其余部分是在所有行一样，那么你可以把它放在group by子句，如果没有，那么你必须做这个结果

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

这是一个连接加入你所要做的，如果数据不等于，你不能把它放在group by子句

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

它应该工作，你可以检查这个问题： Select only one row with max field with One-Many Relationship Table

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