SELECT *FROM R,S where R.a-S.b true false - an index on either R.a or S.b would cause the system to not bring in all records of both tables true false - if all values of R.a are the same then an index would make the SELECT quicker true false - if there is an index on R.a but not S.b then R should get most of the I O buffers true false - if R has an index on field c it would make the SELECT quicker