5. The method of claim 4 , further comprising: if the second key is determined to not match any stored key, compiling, by the computer system, the second query to generate a second query plan, and executing, by the computer system, the second query plan with respect to the second query.
5. The method of claim 4 , further comprising: if the second key is determined to not match any stored key, compiling, by the computer system, the second query to generate a second query plan, and executing, by the computer system, the second query plan with respect to the second query. 7. The method of claim 5 , further comprising: determining, by the computer system, whether the second query plan substantially matches the first query plan; storing, by the computer system, the second query plan in association with the second key if the second query plan is determined to not match the first query plan; and storing, by the computer system, an indication of the second selectivity region in association with the first query plan and the first key if the second query plan is determined to match the first query plan.