连接 3 个表，其中两个有主键，第三个有两个外键

Question

I have three table A, B, C,

Table A is having primary_key a.id_attr and other column is a.id_attr_group.

Table B has one primary key b.id_prod_attr and other column is b.id_prod

Table C

And Third and last one is combination of both keys c.id_attr and c.id_prod_attr in table c their could be multiple entries having 2-3 same rows from both table.

I want to get unique rows those fulfill the condition a.id_attr_group=2 and b.id_prod=1 and those both condition matches in Table C [combinations] I have tried the Inner join, LEFT OUTER JOIN Subquery but no use not able to get the exact results.

Thanks in advance if someone could help me out?

Answer 1

Wait so you have

A

id_attr [PK]
id_attr_group [UNIQUE] (presumably)

B

id_prod_attr [PK]
id_prod [UNIQUE] (presumably)

C

#id_attr [FK from A]
#id_prod_attr [FK from B]

and then I am not really sure about what you're trying to do.

can't you just do

SELECT *
FROM C INNER JOIN B ON B.id_prod_attr = C.id_prod_attr
INNER JOIN A ON A.id_attr = C.id_attr
WHERE A.id_attr_group = 2 and B.id_prod = 1
?

Answer 2

select *

from HomeLoan  -- this table  has the foreign keys
inner join Home on Home.homeNumber = HomeLoan.homeNumber
inner join HomeOwner on HomeOwner.ownerNID = HomeLoan.ownerNID  --3 table join

Where the 3 tables you are joining are HomeLoan , Home and HomeOwner .