SQLite

The following script ends up with the table b-tree for table "parent" containing the integer value 123, and the index b-tree for the PRIMARY KEY of "parent" containing text value "123". A corrupt database.

PRAGMA foreign_keys = true;
CREATE TABLE parent(
  p TEXT PRIMARY KEY
);
CREATE TABLE child(
  c INTEGER UNIQUE,
  FOREIGN KEY(c) REFERENCES parent(p) DEFERRABLE INITIALLY DEFERRED
);

BEGIN;
  INSERT INTO child VALUES(123);
  INSERT INTO parent VALUES('123');
COMMIT;
PRAGMA integrity_check;

The problem is that right before inserting the record into the table b-tree for "parent", the equivalent of "SELECT count(*) FROM child WHERE c='123'" is run to check for foreign key constraint violation resolutions. When integer affinity is applied to the '123', it is also applied to the value that will be inserted into table "parent".

This is a long-standing bug. Has been present since before 3.8.0 (2013).