The SORT BEFORE GROUP BY hint indicates whether the SORT operation occurs before the result set is grouped by the GROUP BY columns.
If the grouped items are few (hundreds of rows), use NO SORT BEFORE. On the other hand, if the grouped items are large (thousands of rows), use SORT BEFORE.
Example:
SELECT --(* vendor(SOLID), product(Engine), option(hint) -- SORT BEFORE GROUP BY *)-- AVG(I) FROM TAB1 WHERE I > 10 GROUP BY I2