How do I get every permutation in two totally unrelated tables with t-sql

Question

I have two tables that are indirectly related by another table

TableA - ID, SomeFieldA

TableB - ID, SomeFieldB

TableAB - IDA, IDB, SomeFieldAB

I have to generate data from the ground up. So I've put some data in TableA, and I've put some data in TableB. The problem is, I need to insert data into TableAB now, and I don't know how to generate a script that will do all the permutations of TableA and TableB together.

For instance:

Table A has two records:

1, 'A'

2, 'AA'

Table B has two records:

3, 'B'

4, 'B'

I want to insert the following data into TableAB:

1, 3, 'first perm'

1, 4, 'second perm'

2, 3, 'third perm'

2, 4, 'fourth perm'

What's the easiest way to do this?

Answer 1

 INSERT TableAB
 SELECT A.ID 'IDA', B.ID 'IDB'
      , A.SomeFieldA+" "+B.SomeFieldB  'SomeFieldAB' 
 FROM A, B

A join without any conditions does all the permutations

Answer 2

You can do this:

select
    a.*, b.*
from
    a, b

This will do a cross join which will give you all possible combinations.

From there, it's simple to use that within the context of an INSERT statement to populate your AB table.

Answer 3

Don't use the ancient join syntax: FROM A, B, use a proper join:

DECLARE @TableA table (Col1 varchar(5), Col2 varchar(5))
DECLARE @Tableb table (Col1 varchar(5), Col2 varchar(5))

INSERT INTO @TableA VALUES ('a','a')
INSERT INTO @TableA VALUES ('aa','aa')

INSERT INTO @TableB VALUES ('b','b')
INSERT INTO @TableB VALUES ('BB','BB')

SELECT
    *
    FROM @TableA
        CROSS JOIN @TableB
    ORDER BY 1

OUTPUT

Col1  Col2  Col1  Col2
----- ----- ----- -----
a     a     b     b
a     a     BB    BB
aa    aa    b     b
aa    aa    BB    BB

(4 row(s) affected)

this will also produce the same result set:

SELECT
    *
    FROM @TableA
        JOIN @TableB ON 1=1
    ORDER BY 1