In yesterday’s blog post, I wrote about creating a table with an IDENTITY value. But the Oracle 12c new feature that I like better is allowing a sequence to be the number generator for the default value of a column. To see what I mean, look at this example:
SQL> create sequence test_seq; Sequence created. SQL> create table test_tab (id number default test_seq.NEXTVAL, val varchar2(20)); Table created.
As you can see, the ID column of my test table has a DEFAULT clause which uses the NEXTVAL of the sequence I created. Now let’s insert some data into the table.
SQL> insert into test_tab (val) values ('first row');
1 row created.
SQL> insert into test_tab (val) values ('second row');
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SQL> commit;
Commit complete.
SQL> select * from test_tab;
ID VAL
---------- --------------------
1 first row
2 second row
As you can see, the Oracle sequence was used to populate the values. At first glance, this would make life easier for the data modeler because one would not need to go the traditional route of coding a trigger to generate the NEXTVAL and assigning this value to the column. However, this autopopulation of the column value with the sequence only works if you do not specify a value, if you let it default. If you explicitly state the value, this method will not use the sequence. A trigger, if coded properly, would force the use of the sequence’s next value for the column.
