Autoincrement in oracle to already created table

On 11g and prior, create a sequence to increment the column via trigger. See Auto-increment primary key in Pre 12c releases (Identity functionality)

For example,

TABLE

SQL> CREATE TABLE t (
  2    ID           NUMBER(10)    NOT NULL,
  3    text  VARCHAR2(50)  NOT NULL);

Table created.

PRIMARY KEY to be populated by the sequence

SQL> ALTER TABLE t ADD (
  2    CONSTRAINT id_pk PRIMARY KEY (ID));

Table altered.

SEQUENCE to support the primary key

SQL> CREATE SEQUENCE t_seq
  2  START WITH 150111111
  3  INCREMENT BY 1;

Sequence created.

TRIGGER If you do not want to have the sequence in the INSERT , you could automate it via TRIGGER.

SQL> CREATE OR REPLACE TRIGGER t_trg
  2  BEFORE INSERT ON t
  3  FOR EACH ROW
  4  WHEN (new.id IS NULL)
  5  BEGIN
  6    SELECT t_seq.NEXTVAL
  7    INTO   :new.id
  8    FROM   dual;
  9  END;
 10  /

Trigger created.

INSERT

SQL> INSERT INTO t(text) VALUES('auto-increment test 1');

1 row created.

SQL> INSERT INTO t(text) VALUES('auto-increment test 2');

1 row created.

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

SQL> SELECT * FROM t;

        ID TEXT
---------- --------------------------------------------------
 150111111 auto-increment test 1
 150111112 auto-increment test 2

SQL>

So, the ID column now starts with value 150111111 and increments by 1 with subsequent inserts.

On 12c , use Identity column. See IDENTITY column autoincrement functionality in Oracle 12c

For example,

TABLE with IDENTITY COLUMN

SQL> CREATE TABLE t
  2    (
  3      ID NUMBER GENERATED ALWAYS AS IDENTITY
  4      START WITH 150111111 INCREMENT BY 1,
  5      text VARCHAR2(50)
  6    );

Table created.

INSERT

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

1 row created.

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

SQL> COLUMN text format A40
SQL> SELECT * FROM t;

        ID TEXT
---------- ----------------------------------------
 150111111 This table has an identity column

So, the ID column now starts with value 150111111 and increments by 1 with subsequent inserts.

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

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> 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: 150111111, INCREMENT BY: 1, 
                                            MAX_VALUE:9999999999999999999999999999, 
                                            MIN_VALUE: 1, CYCLE_FLAG: N, CACHE_SIZE: 20, 
                                            ORDER_FLAG: N

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