1  CHANGE_RELATION
   Changes the definition of the fields and relation-specific
   constraints that make up a relation. You can add, delete, or
   change fields and relation-specific constraints in an existing
   relation. When you execute this statement, Oracle Rdb modifies the
   named field and relation-specific constraint definition(s) within
   the relation definition. All the fields that you do not mention
   remain the same.

   Example:


   RDO> CHANGE RELATION EMPLOYEES.
   cont>     DEFINE SALARY.
   cont> END EMPLOYEES RELATION.
   RDO> !
   RDO> CHANGE RELATION DEPARTMENTS.
   cont>    CHANGE DEPARTMENT_NAME
   cont>        QUERY_NAME FOR DATATRIEVE IS "DEPT".
   cont> END DEPARTMENTS RELATION.
 

2  More
   To change a relation with the CHANGE RELATION statement, you need
   the Oracle Rdb CHANGE privilege for the relation.

   When you execute this statement, Oracle Rdb modifies the named
   field and relation-specific constraint definition(s) within the
   relation definition. All the fields and constraints that you do
   not mention remain the same.

   When you change a relation definition, other users see the
   revised definition only after they invoke the database the next
   time. By default, a database can be opened automatically (that
   is, by any user who invokes the database and executes a data
   manipulation language statement). If the database was modified
   so that it must be manually opened, the RMU/OPEN command must be
   used to open it.

   You must execute the CHANGE RELATION statement in a read/write
   transaction. If you issue this statement when there is no active
   transaction, Oracle Rdb starts a read/write transaction implicitly.

   Other users are allowed to be attached to the database when you
   issue the CHANGE RELATION statement.
 

2  Format

 (B)0CHANGE RELATION qq> name qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqk
      lqqqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqqqqqqqj
      mwqwqqqqqqqqqqqqqqqqqqqqq>qqqqqqqqqqqqqqqqqqqqwqwqwqk
       x tq> DELETE CONSTRAINT w> constraint-name qwj x x x
       x x                     mqqqqqqqq , <qqqqqqqj  x x x
       x mq> relation-constraint-def qqqqqqqqqqqqqqqqqj x x
       mqqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqqqqqj x
      lqqqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqqqqqqqj
      mqqqqwqqqqqqqqqqqqqqqqqq>qqqqqqqqqqqqqqwqqqq> . qqqk
           mq> DESCRIPTION IS /* text */ qqqqj           x
      lqqqqqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqqqqj
      mqwqqqqqqqqqqqqqqqqqqqqqqq>qqqqqqqqqqqqqqqqqqqqqqqqwqk
        mqqwqqwqq> DEFINE  qq> define-clause qqqwq> . qwqj x
           x  tqq> CHANGE  qq> change-clause qqqu      x   x
           x  mqq> DELETE  qq> field-name qqqqqqj      x   x
           mqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqj   x
      lqqqqqqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqqqqqj
      mqqqq> END qqwqqqqq>qqqqwqq> RELATION qqqqqqq> .
                   mq> name qqj

 

3  name
   The name of the relation that you want to modify.
 

3  constraint-name
   The name of an existing relation-specific constraint.
 

3  relation-constraint-def
   Using the relation-constraint-def clause you can name or specify
   the type of relation-level constraints to be defined within a
   specific relation definition.

 (B)0relation-constraint-def =
 qwq> CONSTRAINT constraint-name IS qqwqk
  mqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqj x
 lqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqj
 twq> UNIQUE qqqqqqw>qqw> unique-field-name qqqwqqwqqqk
 xmq> PRIMARY KEY qj   mqqqqqqqqq , qqqq<qqqqqqj  x   x
 tqq> FOREIGN KEY qw> referencing-field-name qwqk x   x
 x                 mqqqqqqqqqqqqq , qqqq<qqqqqj x x   x
 x lqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqqqqqqqj x   x
 x mq> REFERENCES referenced-relation-nameqqqqqqqkx   x
 x           lqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqjx   x
 x           mqqqwqqqqqqqqqqqqqqqqqqqqqqqqqqwqqqqqu   x
 x               mw> referenced-field-name wj     x   x
 x                mqqqqqqqqqq , qqqq<qqqqqqj      x   x
 mqqq> USING rse REQUIRE conditional-expr qqqqqqqqj   x
 lqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqj
 mwqqqqqqqqqqqqqqqqqqqqqqqqqwq>
  m> CHECK ON qwqq> COMMIT qu
               mqq> UPDATE qj

 

4  Arguments
   Constraint-name must be unique within the database. The
   constraint name can be referred to in other statements such as
   DEFINE RELATION, SHOW CONSTRAINT, and START_TRANSACTION.

   The phrase 'CONSTRAINT constraint-name is' is optional. If you
   specify the keyword CONSTRAINT, you must also provide a name for
   the constraint.
 

3  text
   A text string that adds a comment. You can apply the description
   to the entire relation definition using the DESCRIPTION keyword.
   You can also apply a separate description to each field using the
   text markers before the DEFINE or CHANGE clause.
 

3  DEFINE
   Using the DEFINE option of CHANGE RELATION, you can add a
   globally defined field to a relation. You can also use a local
   field name to refer to that global field. You can also define a
   relation-specific constraint at the field level.

 (B)0define-clause =  qqwqqqqqqqqqqqqqqqwqqqk
                    mq> /* text */ qj   x
   lqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj
   mqqwq> global-field-name qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqwqk
      tq> local-field-name qq> BASED ON q> global-field-name qj x
      x    lqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj
      x    mwqqqqqqqqqqqqqqqqqwqwqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqk
      x     mqw> dtr-clause qwj mqqw> field-constraint-def qwqqqu
      x       mqqqqqq<qqqqqqqj     mqqqqqqqqqq<qqqqqqqqqqqqqj   x
      x                                                         x
      mq> local-field-name qq> COMPUTED BY q> value-expr qk     x
        lqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj     x
        mqqqwqqqqqqqqqqqqqqqqqqwqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqvq>
            mqw> dtr-clause qwqj
              mqqqqqq<qqqqqqqj

 

4  Arguments
   The action of CHANGE RELATION with the DEFINE-CLAUSE depends on
   the define-clause, as follows:

   o  DEFINE global-field-name-includes an existing global field
      definition in the relation

      If you include only a name with the DEFINE option, Oracle Rdb
      searches for a field with that name in the list of global
      field definitions for the database. If such a field definition
      exists, Oracle Rdb adds that field definition to the relation
      definition. If no field has that name, Oracle Rdb returns an
      error message.

   o  DEFINE local-field-name BASED ON global-field-name-includes
      an existing field definition in the relation, but gives it a
      local name

      If you include the BASED ON qualifier, Oracle Rdb uses the
      definition specified by the global-field-name syntax.
      However, the name of the new field in the relation is the
      one specified by the local-field-name syntax. This local name
      does not become part of the global list of field names for the
      database.

      You can specify local DATATRIEVE support clauses for the field
      specified with the local-field-name syntax. If you do, this
      local specification overrides the DATATRIEVE clauses attached
      to the global-field-name.

   o  DEFINE local-field-name COMPUTED BY expression-adds a new
      virtual field

      The COMPUTED BY qualifier causes Oracle Rdb to calculate the
      field's value at run time, based on the specified expression.

      You can specify local DATATRIEVE support clauses on any of
      these fields. For more information on the DATATRIEVE clauses,
      ask for HELP on Field_attr.

   o  If you include the DEFINE CONSTRAINT clause, Oracle Rdb defines
      the specified relation-specific constraint.
 

4  field-constraint-def
   Using the field-constraint-def clause you can name or specify the
   type of field-level constraints to be defined within a specific
   relation definition.

 (B)0field-constraint-def =
 qwqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqwqk
  mq> CONSTRAINT constraint-name IS qqj x
 lqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqj
 mwq> NOT MISSING qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqwqk
  tq> UNIQUE qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqu x
  tq> PRIMARY KEY qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqu x
  mw> REFERENCES referenced-relation-name qwqqqqqqqqqqqqqqqqqqqqqqqqwu x
   x                                       m> referenced-field-name jx x
   x                                                                 x x
   mq> USING rse REQUIRE conditional-expr qqqqqqqqqqqq>qqqqqqqqqqqqqqj x
                                                                       x
 lqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj
 mwqqqqqqqqqqqqqqqqqqqqqqqqqqqwq>
  mqq> CHECK ON qwqq> COMMIT qu
                 mqq> UPDATE qj

 

5  Arguments
   Constraint-name must be unique within the database. The
   constraint name can be referred to in other statements such as
   DEFINE RELATION, SHOW CONSTRAINT, and START_TRANSACTION.

   The phrase 'CONSTRAINT constraint-name is' is optional. If you
   specify the keyword CONSTRAINT, you must also provide a name for
   the constraint.

   A field constraint definition differs from a relation constraint
   definition in that you cannot repeat referenced field names. See
   the "relation-constraint-def" help subtopic of CHANGE_RELATION
   for more information.
 

3  CHANGE
   The CHANGE RELATION statement with the CHANGE option modifies the
   local attributes of an existing field. Only the attributes you
   specify in the statement change; all others stay as they are.

   For more details, see the Arguments.

   You can change relation-specific constraints using the DELETE
   CONSTRAINT clause of the CHANGE option. Any constraint to be
   changed must be first specifically deleted by name and then re-
   declared.

 (B)0change-clause =
 qwqqqqqqqqq>qqqqqqqqwqqqqk
  mqq> /* text */ qqqj    x
 lqqqqqqqqqq<qqqqqqqqqqqqqj
 mwqq> global-field-name qqqqqqqqqqqqqqqqqqq>qqqqqqqqqqqqqqqqqqwqk
  tqq> local-field-name qqqqqqqqqqqqqqqqqqqq>qqqqqqqqqqqqqqqqqqu x
  mqq> local-field-name qqqqq> BASED ON global-field-name qqqqqj x
 lqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj
 mwqqqqqq>qqqqqqqqqwqwqwqqqqqqqqqqqqqqqqqqqq>qqqqqqqqqqqqqqqqqqqqqqwqwq>
  mw> dtr-clause qwj x tq> DELETE CONSTRAINT qw> constraint-name qwu x
   mqqqqq<qqqqqqqqj  x x                      mqqqqqqqqq , qqqqqqqjx x
                     x mq> field-constraint-def qqqqqqqqqqqqqqqqqqqj x
                     mqqqqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqqj

 

4  Arguments
   The action of the CHANGE RELATION statement with the CHANGE
   option depends on the change-clause as follows:

   o  CHANGE field-name BASED ON global-field-name-gives the
      specified field the attributes of another field

   o  CHANGE field-name dtr-clause-changes DATATRIEVE support
      characteristics

   o  DELETE CONSTRAINT constraint-name-deletes a relation-specific
      constraint from the relation definition

   You can specify local DATATRIEVE support clauses on any of these
   fields. For more information on the DATATRIEVE clauses, ask for
   HELP on Field_attr.
 

3  DELETE
   Deletes the field from the relation. This option deletes the
   field only from the relation definition. The global field
   definition by this name is still defined for the database as a
   whole, and other relations can still refer to it.

   If an existing view, index, constraint, or computed field refers
   to the field, Oracle Rdb returns an error when you try to delete it.

 (B)0DELETE FIELD qqqwqqq> field-name qqqqwqqq> .
                 mqqqq<qqqq , qqqq<qqqj

 

2  Examples
   Example 1

   The following example adds an existing field definition to a
   relation:


   CHANGE RELATION EMPLOYEES.
        DEFINE SALARY.
   END EMPLOYEES RELATION.

   This example simply names an existing global field, whose
   definition becomes part of the definition for the relation.

   Example 2

   The BASED ON clause adds a local field name to a relation:

   CHANGE RELATION EMPLOYEES.
        DEFINE CURRENT_SALARY BASED ON SALARY.
   END EMPLOYEES RELATION.

   This statement performs the same function as in the previous
   example, but uses the BASED ON clause to give a local name to the
   field. The statement assumes that SALARY is defined globally in
   the database.

   Example 3

   You can change the local attributes for a field definition
   inside the CHANGE RELATION statement without changing the global
   attributes of the field for other relations that refer to it. The
   DATATRIEVE support clauses defined locally override those defined
   globally.

   CHANGE RELATION DEPARTMENTS.
       CHANGE DEPARTMENT_NAME
           QUERY_NAME FOR DATATRIEVE IS "DEPT".
   END DEPARTMENTS RELATION.

   This statement changes QUERY_NAME for the DEPARTMENT_NAME
   field, but only for the DEPARTMENTS relation. The definition
   of DEPARTMENT_NAME remains the same for any other relations that
   use it.

   Example 4

   You can change a local field so that it is based on a different
   global field without changing the the name of the local field:

   DEFINE FIELD SALARY
      DATATYPE SIGNED LONGWORD SCALE -2
      VALID IF SALARY > 8000
      MISSING_VALUE IS 0
      EDIT_STRING FOR DATATRIEVE "$$$$$$9.99".

   DEFINE FIELD MONEY
      DATATYPE TEXT SIZE 8
      VALID IF SALARY > 8000
      MISSING_VALUE IS 0
      EDIT_STRING FOR DATATRIEVE "$$$$$$9.99".

   CHANGE RELATION EMPLOYEES.
     DEFINE SALARY.
   END.
   CHANGE RELATION EMPLOYEES.
     CHANGE SALARY BASED ON MONEY.
   END.

   This example assumes two fields, SALARY and MONEY, defined
   globally. They have different data types.

   o  The first CHANGE RELATION statement adds a field to EMPLOYEES
      using the global SALARY field definition

   o  The second CHANGE RELATION statement uses the BASED ON clause
      to substitute the MONEY definition for the global SALARY. The
      local name remains the same, but that name now points to a
      different global definition. There are now two fields named
      SALARY in the database, one local and one global.

   Example 5

   A COMPUTED BY field is calculated from another field in the
   relation:

   CHANGE RELATION SALARY_HISTORY.
      DEFINE SS_DEDUCTION
        COMPUTED BY (SALARY_AMOUNT * 0.0625).
   END SALARY_HISTORY RELATION.

   This statement adds a "virtual" field, whose value is computed
   from other fields.

   Example 6

   The following example deletes a field:

   CHANGE RELATION COLLEGES.
       DELETE CONTACT_NAME.
   END COLLEGES RELATION.

   This example changes the COLLEGES relation by removing the
   CONTACT_NAME field from it. A global field is still defined for
   the database as a whole, and other relations can still refer to
   it. It may have some other name, if CONTACT_NAME were defined
   with the BASED ON qualifier. This statement also makes the data
   associated with that field invisible.

   Example 7

   This example changes the field-level primary key constraint for
   the field DEPT_CODE to a field-level unique constraint.

   RDO> CHANGE RELATION JOB_HISTORY
   cont> DELETE CONSTRAINT JOB_HISTORY_FOREIGN3.
   cont> END.
   RDO> CHANGE RELATION DEPARTMENTS
   cont> DELETE CONSTRAINT DEPARTMENTS_PRIMARY1
   cont> CONSTRAINT DEPARTMENTS_UNIQUE UNIQUE DEPARTMENT_CODE.
   cont> END.

   The example illustrates how constraints can refer to each other.
   Before the primary key constraint DEPARTMENTS_PRIMARY1 can be
   deleted, you must delete the foreign key constraint JOB_HISTORY_
   FOREIGN3.

   Example 8

   The following example shows that objects in the database with a
   dependency on the EMPLOYEES relation must be deleted before the
   EMPLOYEES relation can be deleted:

   RDO> START_TRANSACTION READ_WRITE
   RDO> CHANGE RELATION JOB_HISTORY
   cont>    DELETE CONSTRAINT JOB_HISTORY_FOREIGN1.
   cont> END.
   RDO> CHANGE RELATION SALARY_HISTORY
   cont>    DELETE CONSTRAINT SALARY_HISTORY_FOREIGN1.
   cont> END.
   RDO> CHANGE RELATION DEGREES
   cont>    DELETE CONSTRAINT DEGREES_FOREIGN1.
   cont> END.
   RDO> CHANGE RELATION RESUMES
   cont>   DELETE CONSTRAINT RESUMES_FOREIGN1.
   cont> END.
   RDO> CHANGE RELATION RESUMES
   cont>    DELETE CONSTRAINT RESUMES_UNIQUE_EMPLOYEE_ID.
   cont> END.
   RDO> DELETE TRIGGER EMPLOYEE_ID_CASCADE_DELETE, STATUS_CODE_CASCADE_UPDATE.
   RDO> DELETE VIEW CURRENT_INFO, CURRENT_SALARY, CURRENT_JOB.
   RDO>
   RDO> DELETE RELATION EMPLOYEES.
   RDO> ROLLBACK