ALTER TABLE external

Add, modify or drop columns for an external table.

Syntax:

   ALTER TABLE [schema.]table
      xt_clauses [,…]
         [ENABLE enable_clause | DISABLE disable_clause]
            [PARALLEL parallel_clause]
               [{ENABLE|DISABLE} TABLE LOCK]
                  [{ENABLE|DISABLE} ALL TRIGGERS]
                      REJECT LIMIT {int | UNLIMITED};

xt_clauses:
   ADD column datatype [DEFAULT expr] [column_constraint(s)]
     [table_constraint] [table_ref_constraint] [lob_storage]

   SET UNUSED (column [,…])
      [CASCADE CONSTRAINTS ][INVALIDATE]

   DROP COLUMN column
      [CASCADE CONSTRAINTS] [INVALIDATE] CHECKPOINT int

   DROP (column [,…])
      [CASCADE CONSTRAINTS] [INVALIDATE] CHECKPOINT int

   DROP COLUMNS CONTINUE [CHECKPOINT int]

   DROP UNUSED COLUMNS [CHECKPOINT int]

   MODIFY column datatype [DEFAULT expr] [column_constraint(s)]

   MODIFY column [NOT] SUBSTITUTABLE AT ALL LEVELS [FORCE]

   DEFAULT DIRECTORY directory [ACCESS PARAMETERS {USING CLOB subquery | (opaque_format_spec) }]
      LOCATION (directory:'location_specifier' [,directory2:'location_specifier2'…)

Examples

Add a column to a table
   ALTER TABLE STAFF_OPTIONS
      ADD SO_INSURANCE_PROVIDER Varchar2(35);

Add  a default value to a column
   ALTER TABLE STAFF_OPTIONS
      MODIFY SO_INSURANCE_PROVIDER Varchar2(35) DEFAULT 'ABC Ins';

Add two columns to a table and remove a constraint
   ALTER TABLE STAFF_OPTIONS
      ADD (SO_STAFF_ID INT, SO_PENSION_ID INT)
          STORAGE INITIAL 10 K
          NEXT 10 K
          MAXEXTENTS 121
          PCTINCREASE 0
          FREELISTS 2
      DROP CONSTRAINT cons_SO;

"The abyss between rational and the spiritual, the external and the internal, the objective and the subjective, the technical and the moral, the universal and the unique, constantly grows deeper" ~ Vaclav Havel

Related Commands:

ANALYZE TABLE COMPUTE STATISTICS
ALTER INDEX
ALTER VIEW
COMMENT - Add a comment to a table or a column.
RENAME
DBMS_REDEFINITION

Related Views:

  DBA_ALL_TABLES       ALL_ALL_TABLES       USER_ALL_TABLES
  DBA_EXTERNAL_TABLES  ALL_EXTERNAL_TABLES  USER_EXTERNAL_TABLES
  DBA_TABLES           ALL_TABLES           USER_TABLES         TAB
  DBA_TAB_COLUMNS      ALL_TAB_COLUMNS      USER_TAB_COLUMNS 
  DBA_PART_TABLES      ALL_PART_TABLES      USER_PART_TABLES 


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