IDENTITY column autoincrement functionality in Oracle 12c

Oracle 12c has introduced the IDENTITY column which is the automatic method over the old trigger-sequence based approach to auto-populate the primary key of a table. In my previous post, Auto-increment primary key in Pre 12c releases (Identity functionality) , I demonstrated the trigger-sequence based approach. now let’s see the new way in 12c –

TABLE with IDENTITY COLUMN

    SQL> CREATE TABLE t
      2    (
      3      ID NUMBER GENERATED ALWAYS AS IDENTITY
      4      START WITH 1000 INCREMENT BY 1,
      5      text VARCHAR2(50)
      6    );
    
    Table created.
    
    SQL>

INSERT

    SQL> INSERT INTO t
      2    ( text
      3    ) VALUES
      4    ( 'This table has an identity column'
      5    );
    
    1 row created.

    SQL> INSERT INTO t
      2    ( text
      3    ) VALUES
      4    ( 'This table has an identity column'
      5    );
    
    1 row created.
    
    SQL>

Let’s see if we have the ID column auto-incremented with the desired values-

    SQL> COLUMN text format A40
    SQL>
    SQL> SELECT * FROM t;
    
       ID TEXT
    ----- ----------------------------------------
     1000 This table has an identity column
     1001 This table has an identity column
    
    SQL>

So, the ID column now starts with value 1000 and increments by 1 with subsequent inserts.

Oracle creates a sequence to populate the identity column. You can find it named as ISEQ$$

    SQL>
    SQL> SELECT sequence_name,
      2    min_value,
      3    max_value,
      4    increment_by
      5  FROM user_sequences;
    
    SEQUENCE_NAME                   MIN_VALUE  MAX_VALUE INCREMENT_BY
    ------------------------------ ---------- ---------- ------------
    ISEQ$$_94087                            1 1.0000E+28            1
    
    SQL>

More information about the identity columns, use the ALL_TAB_IDENTITY_COLS view.

    SQL>
    SQL> SELECT table_name,
      2    column_name,
      3    generation_type,
      4    identity_options
      5  FROM all_tab_identity_cols
      6  WHERE owner = 'LALIT'
      7  ORDER BY 1,
      8    2;
    
    TABLE_NAME           COLUMN_NAME     GENERATION IDENTITY_OPTIONS
    -------------------- --------------- ---------- --------------------------------------------------
    
    T                    ID              ALWAYS     START WITH: 1000, INCREMENT BY: 1, MAX_VALUE:
                                                     9999999999999999999999999999, MIN_VALUE: 1, CYCLE
                                                    _FLAG: N, CACHE_SIZE: 20, ORDER_FLAG: N
    
    
    SQL>

Hope it helps!