Question

表A具有ID和UnitCost列

    ID           UnitCost
    1            10.00
    2            5.00
    3            1.00

表B具有LotID和ID，它是表A的外键

    LotID         ID From Table A
    A1            1
    A2            1
    A2            2
    A2            2
    A3            3

期望的输出：

    LotID         Total
    A1            10.00
    A2            20.00
    A3            1.00

Answer 1

使用GROUP BY，然后总结单位成本值。这是查询：

SELECT b.LotID, SUM(a.UnitCost) AS Total
FROM tableA a JOIN tableB b ON a.ID = b.ID
GROUP BY b.LotID

Answer 2

首先，您需要使用JOIN MYSQL JOIN两个表，然后您需要对LotID进行分组，然后sum将汇总这样的单播值

select table_b.LoatID , sum(table_a.UnitCast) as total 
from table_a join table_b 
on table_a.ID = table_b.ID 
group_by table_b.LotID ;