Ticket #26347: django_m2m_bug_step_by_step

Setup
======

CREATE TABLE t ( id INT NOT NULL AUTO_INCREMENT, from_id INT, to_id INT, PRIMARY KEY (id) );
INSERT INTO t (from_id, to_id) VALUES (10, 20);

Session A                                               Session B
=========                                               =========

SET autocommit=0;                                       SET autocommit=0;

SELECT * FROM t;                                        SELECT * FROM t;
+----+---------+-------+                                +----+---------+-------+
| id | from_id | to_id |                                | id | from_id | to_id |
+----+---------+-------+                                +----+---------+-------+
|  1 |      10 |    20 |                                |  1 |      10 |    20 |
+----+---------+-------+                                +----+---------+-------+
1 row in set                                            1 row in set

DELETE FROM t WHERE from_id=10;
Query OK, 1 row affected

SELECT * FROM t WHERE from_id=10 and to_id IN (20);
Empty set

INSERT INTO t (from_id, to_id) VALUES (10, 20);
Query OK, 1 row affected

COMMIT;
SET autocommit=1;

                                                        DELETE FROM t WHERE from_id=10;
                                                        Query OK, 1 row affected

                                                        SELECT * FROM t WHERE from_id=10 and to_id IN (20);
                                                        +----+---------+-------+
                                                        | id | from_id | to_id |
                                                        +----+---------+-------+
                                                        |  1 |      10 |    20 |
                                                        +----+---------+-------+
                                                        1 row in set

                                                        (Not inserting anything since "it's already there!")

                                                        COMMIT;
                                                        SET autocommit=1;

Later
=====

SELECT * FROM t;
Empty set