Question

I found in this article, that since ORACLE 10g, there is a way to make a particular connection-session compare strings case-insensitive, without needing any crazy SQL functions, using an ALTER SESSION.

Does anyone know if, in 11g, there might be a way to make the database to always operate in this mode by default for all new connection-sessions, thereby eliminating the need for running ALTER SESSIONs every time you connect?

Or perhaps, an additional parameter you could specify on your connection string that would turn the same on?

Answer 1

You could just set the NLS_SORT, NLS_COMP parameters mentioned in the article as the values in the the Oracle init file using the alter system set <parameter> = <value>; clause.

Info on using the alter system commands can be found here.

Here is a good link on the correct usage of the NLS_* parameters. Note that some settings of of the NLS_SORT parameter can/could cause performance issues, namely when it is not set to BINARY. The Oracle docs state:

Setting NLS_SORT to anything other than BINARY causes a sort to use a full table scan, regardless of the path chosen by the optimizer. BINARY is the exception because indexes are built according to a binary order of keys. Thus the optimizer can use an index to satisfy the ORDER BY clause when NLS_SORT is set to BINARY. If NLS_SORT is set to any linguistic sort, the optimizer must include a full table scan and a full sort in the execution plan.

Answer 2

Sure you can!

Get your friendly DBA to set these parameters:

ALTER SYSTEM SET NLS_COMP=LINGUISTIC SCOPE=SPFILE; 

ALTER SYSTEM SET NLS_SORT=BINARY_AI SCOPE=SPFILE;

This is taken from my short article on How to make Oracle Case Insensitive

Answer 3

I tried using a logon trigger to issue these commands to get case-insensitive queries:

execute immediate  alter session set NLS_SORT=BINARY_CI ;
execute immediate  alter session set NLS_COMP=LINGUISTIC ;

And while that did give me CI, it also gave me unbelievably bad performance issues. We have one table in particular that, without those settings, inserts take 2 milliseconds. With those settings in place, inserts took 3 seconds. I have confirmed this by creating and dropping the trigger multiple times.

I don t know if doing it at the system level, as opposed to the session level with a trigger, makes a difference or not.

Answer 4

I found the same performance issue with inserts and nls in 11g r2! Luckily for me the performance hit was not significant enough requiring an app change.

If you can do without binary_ci for the INSERT, then I would do an alter session just before the insert and afterwards, so you don t have to drop the trigger

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