3 summary

Week 6 Query Processing and Optimization Techniques

Query Processing

Translating SQL queries into RA

Evaluation Plan

Query Execution

Query Optimization

Translation Rules

Cost Estimations

summary Real-life example quiz



Let us take an example of a database with the following tables: Book (Book No, Book Title) Member (Member No, Member Name) Loan(Book No, Member No, Loan Date) Let us say we had lost a book whose title is ‘Zeus’ and we want to know the name of the member who was its last borrower. Meanwhile we have 300000 members, 10,000,000 books and 500,000,000 records about loans.

There are many ways of finding the name of the member who was its last borrower.• Making the Cartesian product of Book, Member and Loan before

looking for the title ‘Zeus’ and then the borrower.• Making the Cartesian product of Book and Loan before looking the title ‘Zeus’.

Then make a join of the result with Member for checking who the last borrower was.



• Making the Cartesian product of Member and Loan. Then make a join of the result with Book for checking what the book was and who the last borrower was.

• Looking for the book ‘Zeus’ in Book, then looking for the book ‘Zeus’ in Loan this will give the ‘Member No’ and at the end use the ‘Member No’ in Member to find the name of the member.

• Etc.

Among the different solutions attempted, some are more optimized than others. For instance, making the Cartesian product of all tables before looking for the title ‘Zeus’ and then the borrower is the longest way to find the answer since it will generate 300,000*10,000,000*500,000,000 records among which to look for one answer.

Finding the shortest way that consume less resources than other ways and executes faster than others is the goal of Query processing and Optimization Techniques.

1. What is query processing? A. The activities involved in entering in a database. B. The activities involved in creating a database. C. The activities involved in retrieving data from the database. D. The activities involved in modifying a database.

2. What is relational algebra? A. The basic set of operations for the relational model B. SQL C. DML D. The activities involved in modifying a database.

3. Query optimization is a function of many relational database management systems in which multiple query plans for satisfying a query are examined and a good query plan is identified: A. True B. False



Enter answer,,,. 1. 2. 3.

1. What is query processing? A. The activities involved in entering in a database. B. The activities involved in creating a database. C. The activities involved in retrieving data from the database. D. The activities involved in modifying a database.

2. What is relational algebra? A. The basic set of operations for the relational model B. SQL C. DML D. The activities involved in modifying a database.

3. Query optimization is a function of many relational database management systems in which multiple query plans for satisfying a query are examined and a good query plan is identified: A. True B. False



Enter answer,,,. 1. C 2. B 3. A

4. What is not a translation rule? A. Cascade of select B. Commutativity of select C . Cascade of project D. Commuting select with join E. Commuting rename

5. Cost estimations is the process of estimating and comparing costs of executing query using different execution strategies: A. True B. False


answer is: 4. 5.


4. What is not a translation rule? A. Cascade of select B. Commutativity of select C . Cascade of project D. Commuting select with join E. Commuting rename

5. Cost estimations is the process of estimating and comparing costs of executing query using different execution strategies: A. True B. False


answer is: 4. E 5. A


Education

3 summary