if today is None, then no censoring
    otherwise replace each column with:
        CASE WHEN {date_column} < '{today}' THEN {column} ELSE null END

def date_censor_sql(date_column, today, column=None):
    """
    if today is None, then no censoring
    otherwise replace each column with:
        CASE WHEN {date_column} < '{today}' THEN {column} ELSE null END
    """
    if column is None:
        column = date_column

    if today is None:
        return column
    else:
        return "(CASE WHEN {date_column} < '{today}' THEN {column} ELSE null END)".format(
                date_column=date_column, today=today, column=column)