I don't claim to be an expert on the subject, but when faced with a query like this:

SELECT field

FROM table

WHERE (field LIKE '%A%') OR (field LIKE '%B%')

I find I get much better performance if I do this...

SELECT field

FROM table

WHERE (field LIKE '%A%')

UNION

SELECT field

FROM table

WHERE (field LIKE '%B%')

INTERSECT and EXCEPT can also be used, along with the judicious application of parentheses, to get the results you desire. It's worked quite well for me on a number of occasions, though I've never tried it with huge data sets.

ron