Hello, I'm using FB 1.5

I have a table with an index on MY_CHAR_FIELD
if I do:

SELECT * FROM MY_TABLE WHERE MY_CHAR_FIELD STARTING WITH 'SOMETHING'

FB perform index reads, bu if I do

SELECT * FROM MY_TABLE WHERE Upper(MY_CHAR_FIELD) STARTING WITH 'SOMETHING'

FB don't use any index, which seems logical.
Can I create an index based on Upper(MY_CHAR_FIELD) ?
How is the correct way to do it ?

Thanks!

-sergio