Mysql 如何对查询的3个表求和？

如果C表是custid1和prodid1，我想得到表A上的txnVolume之和？谢谢你们的帮助！干杯

尝试以下操作：

A table
--------------------
id bId        txnVolume
1  1(b table) 10.00
2  1          5.00
3  2          7.00
4  3          2.00

B table
--------------------
id cId
1  1(C table)
2  2
3  3

C table
--------------------
id cusId prodId
1  1     1
2  1     2
3  1     1
4  1     2

Select sum(coalesce(txnVolume,0))
FROM A INNER JOIN B on A.BID = B.Bid
INNER JOIN C on C.ID = B.CID
WHERE C.CustID = 1 and C.ProdID = 1

请尝试以下操作：

Select sum(coalesce(txnVolume,0))
FROM A INNER JOIN B on A.BID = B.Bid
INNER JOIN C on C.ID = B.CID
WHERE C.CustID = 1 and C.ProdID = 1

---

在sql中，您需要联接表。当表被连接时，它们会创建一个大表。然后可以将where子句添加到列中

select sum(txnVolume) from A
   join B on A.bID = B.id
   join C on C.cID = C.id
  where prodID = 1 and custID = 1

---

在sql中，您需要联接表。当表被连接时，它们会创建一个大表。然后可以将where子句添加到列中

select sum(txnVolume) from A
   join B on A.bID = B.id
   join C on C.cID = C.id
  where prodID = 1 and custID = 1

---

我可以很容易地为您编写此查询，但请告诉我们您的尝试。在mysql查询中如何将表“链接”在一起？请考虑：我可以很容易地为您编写此查询，但请告诉我们您的尝试。在mysql查询中如何将表“链接”在一起？请考虑：

SELECT  SUM(a.txnVolume) totals
FROM    tableA a
        INNER JOIN tablB b
            ON a.bid = b.id
        INNER JOIN tableC c
            ON b.cid = c.ID
WHERE   c.custID = 1 AND c.prodID = 1