code: def parse_column_key_value(table_schema, setting_string):
          
          if ':' in setting_string:
              # splits <column>:<key>=<value> into <column> and <key>=<value>
              column, value = setting_string.split(':', 1)
          elif '=' in setting_string:
              # splits <column>=<value> into <column> and <value>
              column, value = setting_string.split('=', 1)
          else:
              # stores <column> and <value>=None
              column = setting_string
              value = None
  
          if value is not None:
              type_ = table_schema.columns[column].type
              value = datum_from_string(type_, value)
  
          return column, value
docs: Parses 'setting_string' as str formatted in <column>[:<key>]=<value>
          and returns str type 'column' and json formatted 'value'