SQL Server 2019

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create table a (id int, foo int);
create table c (id int);
insert into a values (1,1),(2,2),(3,3);
insert into c values (10),(20);
5 rows affected

select * from a, c


id
foo
id


1
1
10

2
2
10

3
3
10

1
1
20

2
2
20

3
3
20


select * from a cross join c


id
foo
id


1
1
10

2
2
10

3
3
10

1
1
20

2
2
20

3
3
20