March 30, 2010
A continuation of the concept of yesterday’s true or false quiz – this one is a little easier, with new reading material. Today’s quiz is on the topic of improving performance of SQL statements. The reading material:
Article 8 (actually a book)
Article 9 (actually a book)
Article 10 (actually a book)
Please read the above articles and see if you are able to answer the following true or false questions, assuming that the questions apply to a release of Oracle that has been available for up to five years. State why you believe that the answer to the question is true, or why you believe that the answer to the question is false. Any answers that attempt to utilize logical fallacies will be scored as incorrect. (Most of these questions can be answered with the help of the first couple of links.)
1. Queries containing subqueries should be rewritten as a logical step in improving query performance.
2. Complex queries should be decomposed into multiple queries using global temp tables and/or WITH clauses as a step toward improving query performance.
3. Significant performance improvements, possibly 20 fold, are possible by replacing some or all of a SQL statement with PL/SQL. If true, provide an example showing a significant performance improvement with such a replacement. If not true, provide an example that shows that performance did not improve significantly.
4. There are cases were performance improvements are possible by modifying a SQL statement containing a three table equijoin, which accesses primary and foreign keys columns of the tables, into a SQL statement which accesses a single table with two PL/SQL functions (each containing a SELECT) in column positions.