In this post I will put 5 other new 12c features in the spotlight (in addition to the features of a previous post), that really makes the 12c an improvement against the previous versions of the Oracle database.
To get this result I listed up all the major new features and wanted to know my top 5 features that would make my life easier(as a developer), excluding the features from the previous post (I certainly would have added the sequence modification(feature 1)), when doing development on an Oracle database.
- Top end query -> I really like this feature and I’m still wondering why it took Oracle so long before creating it. It is something I could have used a lot in the past, but instead I had to create far too complicated, not as nice readable queries to achieve this. How does it work? Well it’s very easy and it’s readable and can be used in a wide variety of cases. Some examples:
Only get the first 3 rows:
select * from X order by id fetch first 3 rows only;
Skip the first 3 rows and get the next 3 rows:
select * from X order by id offset 3 rows fetch next 3 rows only;
Get the first 50% of records
select * from X order by id fetch first 50 percent rows only;
Get the first 3 rows together with the records equal to these department id’s
select * from emp order by deptno fetch first 3 rows with ties;
If you want the capture the last rows, you can obviously change ‘first’ with ‘last’…
- In the 12c database the use of 32767 characters for a VARCHAR2 in SQL is now available instead of the maximum of 4000(this is also the case for RAW and nvarchar2).
We all have been waiting a long time for this one and before we had to use the clob datatype.
But beware this is not an out of the box feature, you will have to execute the lines below before this is enabled :
shutdown immediate startup upgrade alter system set max_string_size=EXTENDED scope=both; @<ORACLE_HOME>/rdbms/admin/utl32k.sql Shutdown immediate Startup
More info can be found on: http://docs.oracle.com/cd/E16655_01/server.121/e17615/refrn10321.htm
- The invisible column is a feature of which I was wondering where I could use it for.
Well it could be handy when you are adding a column to your table, but you don’t want any existing code to be impacted by it.
Another case where it could be useful, is when using audit columns. Columns as the creation_dt, update_dt, user_creation and user_update will only be of any added value when you would like to audit a certain column.
Packages with inserts, updates, references to this table will not be impacted by the creation of this column.
On the other hand there is also a risk that you forget that this column is in there, because you have to explicitly call for it (a describe or select * will not show this column). You can create invisible columns like this:
ALTER TABLE ADD INVISIBLE;
If you want to make the column visible again, use this:
ALTER TABLE MODIFY VISIBLE;
In summary it could be handy, but don’t forget this column or it will pollute your table.
- The with clause inline plsql feature is also something that I think is very welcome.
It will make it possible to create a procedure or function inside your select statement instead of having to create this in a package or function. Oracle also says that this will optimize the performance against having to call a schema procedure/function(I still have to test this).
A little example:
WITH FUNCTION fnc$_add_one(p_num IN NUMBER) IS BEGIN RETURN p_num+1; END; SELECT fnc$_add_one(1) FROM DUAL;
- Most of the time I use the ANSI way of writing for a left outer join, but the oracle way of writing left outer joins is still often used by many of the oracle developers.
But there was one thing that you could do in ANSI, that you couldn’t in the oracle way. You couldn’t write multiple tables on the left of an outer join, untill12c…
In 11g and before when coding something like this:
select * from a,b,c where a.id = b.id and a.id = c.id(+) and b.id = c.id2(+);
This resulted in -> ORA-01417: a table may be outer joined to at most one other table
In 12c this will work, also the ANSI solution obviously still works both on 12c and on 11g
select * from a JOIN b ON (a.id = b.id) LEFT OUTER JOIN c ON (a.id = c.id AND b.id = c.id2);
Together with the previous post this makes 10 reasons why you should start to use the Oracle 12c database