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