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Tuesday, June 28, 2016

Online table redefination


Online table redefinition of a table


 Lets create a table with some dependent objects for this setup.

DROP PROCEDURE get_description;
DROP VIEW redef_tab_v;
DROP SEQUENCE redef_tab_seq;
DROP TABLE redef_tab PURGE;

CREATE TABLE redef_tab (
  id           NUMBER,
  description  VARCHAR2(50),
  CONSTRAINT redef_tab_pk PRIMARY KEY (id)
);

CREATE VIEW redef_tab_v AS
SELECT * FROM redef_tab;

CREATE SEQUENCE redef_tab_seq;

CREATE OR REPLACE PROCEDURE get_description (
  p_id          IN  redef_tab.id%TYPE,
  p_description OUT redef_tab.description%TYPE) AS
BEGIN
  SELECT description
  INTO   p_description
  FROM   redef_tab
  WHERE  id = p_id;
END;
/

CREATE OR REPLACE TRIGGER redef_tab_bir
BEFORE INSERT ON redef_tab
FOR EACH ROW
WHEN (new.id IS NULL)
BEGIN
  :new.id := redef_tab_seq.NEXTVAL;
END;
/


Lets confirm that objects  are created 


COLUMN object_name FORMAT A20
SELECT object_name, object_type, status FROM user_objects ORDER BY object_name;

OBJECT_NAME          OBJECT_TYPE         STATUS
-------------------- ------------------- -------
GET_DESCRIPTION      PROCEDURE           VALID
REDEF_TAB            TABLE               VALID
REDEF_TAB_BIR        TRIGGER             VALID
REDEF_TAB_PK         INDEX               VALID
REDEF_TAB_SEQ        SEQUENCE            VALID
REDEF_TAB_V          VIEW                VALID

6 rows selected.


Basic Online Table Redefinition

Now we perform an online table redefinition.

-- Check table can be redefined

EXEC DBMS_REDEFINITION.can_redef_table('ATOORPU', 'REDEF_TAB');
--- SCHEMA = ATOORPU, TABLE_NAME=REDEF_TAB


CREATE TABLE redef_tab2 AS
SELECT *
FROM   redef_tab WHERE 1=2;

-- Start Redefinition
EXEC DBMS_REDEFINITION.start_redef_table('ATOORPU', 'REDEF_TAB', 'REDEF_TAB2');


-- Optionally synchronize new table with interim data before index creation
EXEC DBMS_REDEFINITION.sync_interim_table('ATOORPU', 'REDEF_TAB', 'REDEF_TAB2');

-- Add new PK.
ALTER TABLE redef_tab2 ADD (CONSTRAINT redef_tab2_pk PRIMARY KEY (id));

-- Complete redefinition
EXEC DBMS_REDEFINITION.finish_redef_table('ATOORPU', 'REDEF_TAB', 'REDEF_TAB2');

-- Remove original table which now has the name of the new table
DROP TABLE redef_tab2;



Finally, we verify the status of the schema objects.


COLUMN object_name FORMAT A20
SELECT object_name, object_type, status FROM user_objects ORDER BY object_name;

OBJECT_NAME          OBJECT_TYPE         STATUS
-------------------- ------------------- -------
GET_DESCRIPTION      PROCEDURE           VALID
REDEF_TAB            TABLE               VALID
REDEF_TAB2_PK        INDEX               VALID
REDEF_TAB_SEQ        SEQUENCE            VALID
REDEF_TAB_V          VIEW                VALID


Note : The GET_DESCRIPTION procedure and REDEF_TAB_V view are still valid, but the REDEF_TAB_BIR trigger is gone. The trigger was still associated with the original table, renamed to REDEF_TAB2, so when the original table was dropped, the trigger was dropped with it.

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