Comparing table attribute with a string without compromising performance?

Question

in pl/sql what is the best practice for comparing a varchar2 attribute with a string should be case insensetive, without compromising performance.
I've read on using an index (upper(tbl_attribute)) and then comparing in the where clause using
upper(tbl_attribute) = input_value'
is this the only way?
is there a directive that could make the process faster?
how about reading the table into memory then do the compare using upper in memory would that be faster than reading the table each time we run the comaprison condition?
example:
select name from tblnames
where upper(name) = upper('Joe')
thank you

Answer 1

I would say the ideal case would be to ensure that all the data that is stored in the column is upper case to begin with. To monitor that you could place a constraint on the table like the following:
ALTER TABLE TABLE_X ADD CONSTRAINT UPPER_CONS CHECK (COLUMN_X = UPPER(COLUMN_X));If the code can't be modified to always store the data in upper case you could always create a trigger to force the value to be upper case.
Then your WHERE clause would only have to be like the following:
COLUMN_X = UPPER('JOE')In my opinion storing the data as it should be would be the best performing because it should allow the CBO to have as many access paths as possible. You could then create a regular index on this column if there was truly a need for even better performance.
A function-based index as you suggested is another viable option as well.
HTH!