Oracle 21c

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SELECT * FROM v$version


BANNER
BANNER_FULL
BANNER_LEGACY
CON_ID


Oracle Database 21c Express Edition Release 21.0.0.0.0 - Production
Oracle Database 21c Express Edition Release 21.0.0.0.0 - Production
Version 21.3.0.0.0
Oracle Database 21c Express Edition Release 21.0.0.0.0 - Production
0


CREATE TABLE table_1( column_2 VARCHAR2(25)) 
BEGIN
 INSERT INTO table_1 VALUES('red');
 INSERT INTO table_1 VALUES('blue');
 INSERT INTO table_1 VALUES('green');
 INSERT INTO table_1 VALUES('purple');
END;
/
1 rows affected

SELECT * FROM table_1


COLUMN_2


red

blue

green

purple


ALTER TABLE table_1 ADD column_3 INT GENERATED ALWAYS AS IDENTITY
SELECT * FROM table_1


COLUMN_2
COLUMN_3


red
1

blue
2

green
3

purple
4