You can supply additional hint information to the optimizer through a condition hint string.
These per-condition hint strings let users specify additional execution preferences for a condition, which the optimizer follows, if possible. These preferences include which index to use for the condition, the selectivity of the condition, the phase of execution when the condition is executed, and the usefulness of the condition, which affects its ordering among the set of conditions executed within one phase of execution.
Condition hint strings, like the user-supplied selectivity estimates, are supplied within the text of the query by wrapping the condition within parentheses. Then within the parentheses and after the condition, you add a comma and a supply a quoted string containing the desired hints. Within that quoted string each hint appears as a hint type identifier, followed by a colon and the value for that hint type. Multiple hints within the same hint string are separated from each other by a comma, and multiple hints can appear in any order. White space is allowed between any of two elements within a hint string.