Description:
mysql> create table a (a int);
Query OK, 0 rows affected (0.00 sec)
mysql> create table b (b int);
Query OK, 0 rows affected (0.00 sec)
mysql> insert into a values (1),(2);
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> insert into b values (1);
Query OK, 1 row affected (0.00 sec)
mysql> select a from a where a in (select a from a where a in (select b from
b));
+------+
| a |
+------+
| 1 |
| 2 |
+------+
2 rows in set (0.00 sec)
Should return only 1 row (=1)
... because
(select b from b);
+------+
| b |
+------+
| 1 |
+------+
mysql> select a from a where a in (select b from b);
+------+
| a |
+------+
| 1 |
+------+
How to repeat:
See above...