Changes an existing global field definition.  When you use the CHANGE
 FIELD statement to change the attributes of a global field, Rdb/VMS
 changes only the attributes you mention in the statement.  All other
 attributes remain the same.

 Example:

 RDO>  CHANGE FIELD POSTAL_CODE
 cont>    DATATYPE IS TEXT SIZE IS 9 CHARACTERS.

 The CHANGE FIELD statement changes the field definition:

  o  In all the relations that refer to that field
  o  In the data dictionary (if you use INVOKE with the PATHNAME
     qualifier)
  o  In the Rdb/VMS system relations

Additional information available:

MoreFormatExamples

 To change a field using the CHANGE FIELD statement, you need the
 Rdb/VMS CHANGE privilege for the field.

 When you use CHANGE FIELD, you should be aware of the following
 conditions:

  o  If an index is defined on a field that requires a collating
     sequence change, the index must be deleted first, then redefined
     after the collating sequence change.

  o  If the database is created with the DICTIONARY IS REQUIRED
     option, you must invoke the database by path name, rather than
     file name, before you issue this statement.

  o  You cannot issue a CHANGE FIELD statement to change the data type
     or collating sequence for a field that is used in an index or
     view definition.  Rdb/VMS returns an error message in these
     instances and does not change the field.  To change the data type
     or collating sequence of a field used in an index or view, first
     delete the index or view definition, then change the field, and
     finally, redefine the index or view.

 When you change a field definition, this change will be visible to
 other users 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.

 Depending on the type of change you make, you may have to reprocess
 the application programs that refer to the changed fields.

 You can change a field definition only if you have invoked the
 database that includes the field definition.  You must execute this
 statement in a read/write transaction.  If there is no active
 transaction, and you issue this statement, Rdb/VMS starts a
 read/write transaction implicitly.

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

 CHANGE FIELD   ──> name ──┐
               ┌───────────┘
               └──┬───────────────>───────────────┬─┐
                  └─> 
D
E
S
C
R
I
P
T
I
O
N typebox (I)typebox (S) typebox (/)typebox (*) text */ ──┘ │
               ┌──────────────────<─────────────────┘
               └─> field-attributes ──> .

Additional information available:

field-attributes

 field-attributes =

 DATATYPE IS ───> data-type ──┐
    ┌─────────────────────────┘
    └──┬─────────────────────────────────────────────────┬───>
       └┬─┬──> validity-clause───────────────────────┬─┬─┘
        │ ├──> missing-value-clause──────────────────┤ │
        │ ├──> dtr-clause────────────────────────────┤ │
        │ ├──> 
C
O
L
L
A
T
I
N
G
S
E
Q
U
E
N
C
E typebox (I)typebox (S) sequence-name───┤ │
        │ └──> 
N
O 
C
O
L
L
A
T
I
N
G
S
E
Q
U
E
N
C
E ────────────────┘ │
        └─────────────────<────────────────────────────┘

 A list of definitions that indicate what type of data you can store
 in the field and how Rdb/VMS uses that data.  If you do not change a
 field attribute in the CHANGE FIELD statement, the attribute remains
 the same.  The field attributes include the data type and the
 following optional clauses:

  o  VALID IF
  o  MISSING_VALUE
  o  DATATRIEVE support clauses
  o  COLLATING_SEQUENCE

 Do not use multiple, conflicting clauses in a field definition.

 For a complete description of field attributes, ask for HELP on
 Field_attr.

 Example 1

 The following example expands the POSTAL_CODE field to nine
 characters and adds DATATRIEVE support characteristics:

 RDO>  INVOKE DATABASE FILENAME 'MF_PERSONNEL'
 RDO>  SHOW FIELDS POSTAL_CODE
     POSTAL_CODE                      text size is  5
    Description:         Postal code (in US = ZIP)
 RDO> CHANGE FIELD POSTAL_CODE
 cont> DATATYPE IS TEXT SIZE IS 9 CHARACTERS
 cont> DEFAULT_VALUE FOR DTR IS "000000000"
 cont> EDIT_STRING FOR DTR IS "XXXXX-XXXX".
 RDO> SHOW FIELD POSTAL_CODE
      POSTAL_CODE                      text size is  9
    Description:         Postal code (in US = ZIP)
    Edit string:         XXXXX-XXXX
    Default value:       "000000000"
 RDO> FOR E IN EMPLOYEES
 cont>    PRINT E.POSTAL_CODE
 cont>  END_FOR
  03817
  03817
  03301
  03456
    .
    .
    .
  03301
  03809
 RDO>  STORE E IN EMPLOYEES USING
 cont> E.LAST_NAME = "Forester";
 cont> E.EMPLOYEE_ID = "00876";
 cont> E.POSTAL_CODE = "039875573"
 cont> END_STORE
 RDO>  FOR E IN EMPLOYEES
 cont>    WITH E.LAST_NAME = "Forester" OR
 cont>    E.LAST_NAME = "Toliver"
 cont> PRINT
 cont>    E.EMPLOYEE_ID,
 cont>    E.POSTAL_CODE
 cont> END_FOR
  00164   03817
  00876   039875573

 The field remains a text field, but the length is increased to nine
 characters, and an edit string and default value are specified for
 DATATRIEVE.  When you display the data, existing field values are
 padded on the right with spaces.  Thus an existing postal code would
 appear as "03104    ".  Newly stored values can have nine characters.


 Example 2

 The accounting department has decided that the BUDGET field will now
 include pennies:

 RDO> SHOW FIELDS BUDGET
      BUDGET                         signed longword scale  0
    Description:       Generic budget data
    Edit string:       $$$,$$$,$$$
 RDO>  FOR D IN DEPARTMENTS
 cont> WITH D.DEPARTMENT_NAME = 'Manufacturing'
 cont>  PRINT D.BUDGET_ACTUAL
 cont> END_FOR
  BUDGET_ACTUAL
              0
 RDO>  CHANGE FIELD BUDGET
 cont> DATATYPE IS SIGNED LONGWORD SCALE -2
 cont> EDIT_STRING FOR DTR IS "$$$$,$$9.99".
 RDO>  SHOW FIELDS BUDGET
       BUDGET                        signed longword scale  -2
    Description:       Generic budget data
    Edit string:       $$$$,$$9.99
 RDO>  FOR D IN DEPARTMENTS
 cont> WITH D.DEPARTMENT_NAME = 'Manufacturing'
 cont>  PRINT D.BUDGET_ACTUAL
 cont> END_FOR
  BUDGET_ACTUAL
           0.00


 Example 3

 You can add or change a VALID IF clause for a field.  However, if the
 database contains any data that violates the specification of the
 VALID IF clause, the clause is rejected.  The following example shows
 two CHANGE FIELD...  VALID IF statements.  In the first instance, the
 specification is rejected because existing records contain
 EMPLOYEE_ID values less than "98765"; in the second instance, the
 specification is accepted.

 RDO> CHANGE FIELD ID_NUMBER VALID IF ID_NUMBER > "98765".
 %RDB-E-NO_META_UPDATE, metadata update failed
 -RDMS-E-NOT_VALID_FR, field ID in relation CURRENT_INFO fails
 validation
 RDO> CHANGE FIELD ID_NUMBER VALID IF ID_NUMBER > "00050".
 RDO> SHOW FIELD ID_NUMBER
      ID_NUMBER                        text size is  5
    Description:         Generic employee ID
    Missing value:
    Valid:               IF ID_NUMBER > "00050"