ORACLE DDL - CONSTRAINTS

Constraints

   ALTER TABLE [schema.]table
      constraint_clause,...
          [ENABLE enable_clause | DISABLE disable_clause]
              [{ENABLE|DISABLE} TABLE LOCK]
                 [{ENABLE|DISABLE} ALL TRIGGERS];

constraint_clause:
   ADD out_of_line_constraint(s)
   ADD out_of_line_referential_constraint
   DROP PRIMARY KEY [CASCADE] [{KEEP|DROP} INDEX]
   DROP UNIQUE (column,...) [{KEEP|DROP} INDEX]
   DROP CONSTRAINT constraint [CASCADE]
   MODIFY CONSTRAINT constraint constrnt_state
   MODIFY PRIMARY KEY constrnt_state
   MODIFY UNIQUE (column,...) constrnt_state
   RENAME CONSTRAINT constraint TO new_name

constrnt_state:   
    [[NOT] DEFERRABLE] [INITIALLY {IMMEDIATE|DEFERRED}]
       [RELY | NORELY] [USING INDEX using_index_clause]
          [ENABLE|DISABLE] [VALIDATE|NOVALIDATE]
              [EXCEPTIONS INTO [schema.]table]

Añadir una columna a una tabla:
   ALTER TABLE STAFF_OPTIONS
      ADD SO_INSURANCE_PROVIDER Varchar2(35);

Valor por defecto de una columna:
   ALTER TABLE STAFF_OPTIONS
      MODIFY SO_INSURANCE_PROVIDER Varchar2(35) DEFAULT 'ABC Ins';

Añade dos columnas y borrar una restriccion:
   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;