mysql> select * from cnt_test;
+------+
| id   |
+------+
|    1 |
|    2 |
| NULL |
|    4 |
+------+

mysql> select * from join_null_test;
+------+
| id   |
+------+
|    1 |
| NULL |
+------+
2 rows in set (0.00 sec)


mysql> select * from cnt_test inner join join_null_test on cnt_test.id = join_null_test.id;
+------+------+
| id   | id   |
+------+------+
|    1 |    1 |
+------+------+
1 row in set (0.01 sec)

use test
go

select * from test1;
select * from test2;

select * from test1 inner join test2 on test1.id = test2.id;