Why does SQLite accept a child row whose parent does not exist?

Foreign-key enforcement must be enabled and verified for each relevant SQLite connection. Declaring a constraint alone should not be treated as proof of enforcement. Set PRAGMA foreign_keys = ON at connection initialization before a transaction, then read the setting back. Test an invalid child insert and a parent deletion that should be restricted. Run foreign_key_check when auditing existing data. Enabling enforcement does not automatically repair historical violations. Connection pools and migration tools need the same initialization policy, and changing the pragma inside an active transaction does not provide the intended switch. Minimal example:

import sqlite3
db = sqlite3.connect(":memory:")
db.execute("PRAGMA foreign_keys = ON")
db.executescript("""
CREATE TABLE parent(id INTEGER PRIMARY KEY);
CREATE TABLE child(parent_id INTEGER REFERENCES parent(id));
""")
try:
    db.execute("INSERT INTO child VALUES (?)", (999,))
except sqlite3.IntegrityError:
    db.rollback()
else:
    raise AssertionError("Missing parent was accepted")
finally:
    db.close()