This article focus on two hints:
USE_CONCAT - The
USE_CONCAT hint forces combined
OR conditions in the
WHERE clause of a query to be transformed into a compound query using the
ALL set operator. Generally, this transformation occurs only if the cost of the query using the concatenations is cheaper than the cost without them.
NO_EXPAND - The
NO_EXPAND hint prevents the cost-based optimizer from considering
OR-expansion for queries having
OR conditions or
IN-lists in the
WHERE clause. Usually, the optimizer considers using
OR expansion and uses this method if it decides that the cost is lower than not using it.
NO_EXPAND can be forced by alter session for all statements
ALTER SESSION SET "_no_or_expansion" = TRUE;