import sqlite3


def migrate(conn: sqlite3.Connection):
    columns = conn.execute("PRAGMA table_info(posts)")
    column_names = [col[1] for col in columns]
    if "reposted_id" not in column_names:
        _ = conn.execute("""
            ALTER TABLE posts
            ADD COLUMN reposted_id INTEGER NULL REFERENCES posts(id) ON DELETE SET NULL
        """)