The RDB$RELATION_CONSTRAINTS system table lists all table-
    specific constraints. The following table provides information
    on the columns of the RDB$RELATION_CONSTRAINTS system table.

                                Data
    Column Name                 Type      Summary Description

    RDB$CONSTRAINT_MATCH_TYPE   integer   The match type associated
                                          with a referential
                                          integrity table-specific
                                          constraint. This column is
                                          reserved for future use.
                                          The value is always 0.
    RDB$CONSTRAINT_NAME         char(31)  The name of the constraint
                                          defined by the table
                                          specified by RDB$RELATION_
                                          NAME.

                                          The value in this column
                                          equates to a value for the
                                          same column in the
                                          RDB$CONSTRAINTS system
                                          table.
    RDB$CONSTRAINT_SOURCE       list      This text string contains
                                of byte   the source of the
                                varying   constraint from the table
                                          definition.
    RDB$CONSTRAINT_TYPE         integer   The type of table-specific
                                          constraint defined. The
                                          values are shown in the
                                          RDB$CONSTRAINT_TYPE Help
                                          topic.
    RDB$ERASE_ACTION            integer   The type of referential
                                          integrity erase action
                                          specified. This column is
                                          reserved for future use.
                                          The value is always 0.
    RDB$FIELD_NAME              char(31)  The name of the column
                                          for which a column-level,
                                          table-specific constraint
                                          is defined. The column is
                                          blank for a table-level
                                          constraint.
    RDB$FLAGS                   integer   Flags.
    RDB$MODIFY_ACTION           integer   The type of referential
                                          integrity modify action
                                          specified. This column is
                                          reserved for future use.
                                          The value is always 0.
    RDB$REFD_CONSTRAINT_NAME    char(31)  The name of the unique or
                                          primary key constraint
                                          referred to by a
                                          referential integrity
                                          foreign key constraint.

                                          If the constraint is
                                          not a referential
                                          integrity constraint or
                                          no referential integrity
                                          constraint was specified,
                                          this column will be
                                          null. Otherwise, the
                                          value in this column
                                          will equate to a value
                                          for the same columns in
                                          the RDB$CONSTRAINTS and
                                          RDB$RELATION_CONSTRAINT_
                                          FLDS system tables.

                                          This column is used to
                                          determine the foreign key
                                          referenced table name and
                                          referenced column names.
    RDB$RELATION_NAME           char(31)  The name of the table
                                          on which the specified
                                          constraint is defined.
                                          The value in this column
                                          equates to a value for
                                          the same column in the
                                          RDB$RELATIONS system table.
    RDB$SECURITY_CLASS          char(20)  Reserved for future use.