SQL: Single select query from 2 Non-Joining tables

Question

I have 2 tables which doesn't have any references to each other and I'm trying to create a third table (for reference lookup) by selecting from fields from both tables.

TableA has an A_ID
TableB has a B_ID

I want to create Table C which has a 1 to 1 reference between A_ID to B_ID where A_ID = FirstID and B_ID = SecondID, I can't join the 2 tables because there's nothing in common.

Something like:

Insert INTO [TableC]
(FirstID, SecondID)
SELECT
A_ID As FirstID,
(Select B_ID From TableB)
FROM TableA

Basically we are creating a relationship right now with Table C so that we can use it to reference the two tables in the future using the their IDs.

Answer 1

Assuming TableA and TableB truly have nothing in common, then what you want is the Cartesian product, that is, for every row in A times every row in B.

INSERT INTO TableC(FirstID,SecondID)
SELECT A_ID,B_ID
FROM TableA
CROSS JOIN TableB

Perhaps what you really want is to join them by ROW_NUMBER().

INSERT INTO TableC(FirstID,SecondID)
SELECT A_ID,B_ID
FROM (SELECT A_ID,ROW_NUMBER() OVER (ORDER BY whatever) as rownumA FROM TableA) a
FULL OUTER JOIN (SELECT B_ID,ROW_NUMBER() OVER (ORDER BY whatever) as rownumB FROM TableB) b ON a.rownumA=b.rownumB