乘以主键链接的不同表中的值

Question

I'd like to multiply values from two different tables( transactions.quantity*prices.price ) which are connected by primary keys. I was trying to do it like this: select transactions.idd * prices.price join on discs transactions.idd = discs.idd join on prices discs.idp = prices.idp

Unfortunetely my knowledge from mysql is pretty bad and its obviously not working.

Can somebody help me to fix this query?

Answer 1

You just have to join the tables before doing the multiplications.

SELECT A.quantity, C.price, A.quantity*C.price cost
FROM transactions A JOIN disc B
ON A.idd=B.idd  JOIN prices C
ON B.idp=C.idp;

You did not include the disc table in your join, and the syntax of your query is wrong.