An SQL injection example: query = "SELECT x, y, z FROM Table WHERE id='$id' " If $id is replaced with "'; DELETE FROM Table; SELECT * FROM Table WHERE id='", executing this query will wipe out all the data in Table.
query = "SELECT x, y, z FROM Table WHERE id='$id' " ここで、$idが"'; DELETE FROM Table; SELECT * FROM Table WHERE id='"に補間された場合、このクエリを実行するとテーブルの全てのデータが削除されてしまう。