The following table lists the values for the RDB$FIELD_SUB_TYPE
    and the RDB$PARAMETER_SUB_TYPE columns.

                     RDB$FIELD_TYPE = DSC$K_DTYPE_ADT

    RDB$FIELD_SUB_TYPE [1]      Summary Description

    Less than 0                 Reserved for future use.
    Equal to 0                  Traditional OpenVMS timestamp, which
                                includes year, month, day, hour,
                                minute, second.
    7                           DATE ANSI, which includes year,
                                month, day.
    56                          TIME, which includes hour, minute,
                                second.
    63                          TIMESTAMP, which includes year,
                                month, day, hour, minute, second.
    513                         INTERVAL YEAR.
    514                         INTERVAL MONTH.
    515                         INTERVAL YEAR TO MONTH.
    516                         INTERVAL DAY.
    520                         INTERVAL HOUR.
    524                         INTERVAL DAY TO HOUR.
    528                         INTERVAL MINUTE.
    536                         INTERVAL HOUR TO MINUTE.
    540                         INTERVAL DAY TO MINUTE.
    544                         INTERVAL SECOND.
    560                         INTERVAL MINUTE TO SECOND.
    568                         INTERVAL HOUR TO SECOND.
    572                         INTERVAL DAY TO SECOND.

             RDB$FIELD_TYPE = DSC$K_DTYPE_T or DSC$K_DTYPE_VT

    RDB$FIELD_SUB_TYPE          Summary Description

    Equal to 0                  ASCII or DEC_MCS character set.
    Greater than 0              Character set other than ASCII or
                                DEC_MCS.
    Less than 0                 Special use of character data.

                  RDB$FIELD_TYPE = DSC$K_DTYPE_BLOB [2]

    RDB$FIELD_SUB_TYPE          Summary Description

    Less than 0                 User-specified.
    Equal to 0                  Default.
    Equal to 1                  BLR (query) type.
    Equal to 2                  Character type.
    Equal to 3                  MBLR (definition) type.
    Equal to 4                  Binary type.
    Equal to 5                  OBLR (outline) type.
    Greater than 5              Reserved for future use.

    Footnotes:
    [1]   When RDB$FIELD_SUB_TYPE is not equal to 0, then
          RDB$SEGMENT_LENGTH can hold the interval leading field
          precision for intervals, and RDB$FIELD_SCALE can hold
          the fractional seconds precision for interval, time, or
          timestamp.
    [2]   RDB$SEGMENT_LENGTH is the suggested size for a single
          binary large object (BLOB) segment.