postgresql provides it, msssql (I think) provides it, too. and finally, with release 12c, you may have auto incrementing columns in oracle:
SQL> create table t1 ( a number generated always as identity, b number ); SQL> insert into t1 (b) values (1); 1 row created. SQL> insert into t1 (b) values (2); 1 row created. SQL> select * from t1; A B ---------- ---------- 1 1 2 2
what happens in the background is quite simple: oracle creates a sequence:
SQL> select sequence_name from user_sequences; SEQUENCE_NAME -------------------------------------------------------------------------------- ISEQ$$_19540
user/dba/all_tables has a new column to refect this:
SQL> select HAS_IDENTITY from user_tables where table_name = 'T1'; HAS --- YES
but it is not possible to have more than one of these:
SQL> create table t2 ( a number generated always as identity, b number generated always as identity );
create table t2 ( a number generated always as identity, b number generated always as identity )
*
ERROR at line 1:
ORA-30669: table can have only one identity column
once the table is dropped, the sequence is gone, too:
SQL> drop table t1; Table dropped. SQL> select sequence_name from user_sequences; no rows selected SQL>
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