Does a single read operation.

def read(database, table, key):
    """Does a single read operation."""
    with database.snapshot() as snapshot:
        result = snapshot.execute_sql('SELECT u.* FROM %s u WHERE u.id="%s"' %
                                      (table, key))
        for row in result:
            key = row[0]
        for i in range(NUM_FIELD):
            field = row[i + 1]