DAT 390 Wk 1 – Apply: Labs

Complete zyLab 1.8-1.9 in zyBooks. You have unlimited attempts in Develop mode. Toggle to Submit mode for a grade.

Refer to the film table of the Sakila database. This lab loads film with 100 rows from Sakila. Consequently, SELECT * FROM film; generates too many characters to display in the zyLab environment. However, statements with less output, such as SELECT title FROM film;, execute successfully.

This lab illustrates the use of indexes and EXPLAIN to optimize query performance. Refer to EXPLAIN documentation for information about EXPLAIN result columns.

Write and run seven SQL statements:

1. Explain the query SELECT * FROM film WHERE title = ‘ALONE TRIP’;.

In the EXPLAIN result, column key is null, indicating no index is available for the query. Column rows is 100, indicating all rows are read. The query executes a table scan and is slow.

2. Create an index idx_title on the title column.
3. Explain the query of step 1 again.

In the EXPLAIN result, column key has value idx_title, indicating the query uses the index on title. Column rows is 1, indicating only one table row is read. The query is fast.

4. Explain the query SELECT * FROM film WHERE title > ‘ALONE TRIP’;.

In the EXPLAIN result, column key is null, indicating the query does not use the idx_title index. Column rows is 100, indicating all rows are read. Since the query has > in the WHERE clause rather than =, the query executes a table scan and is slow.

5. Explain the query SELECT rating, count(*) FROM film GROUP BY rating;

In the EXPLAIN result, column key is null, indicating no index is available for the query. Column rows is 100, indicating all rows are read. The query executes a table scan and is slow.

6. Create an index idx_rating on the rating column.
7. Explain the query of step 5 again.

In the EXPLAIN result, column key has value idx_rating, indicating the query reads rating values from the index. The query uses an index scan, which is faster than a table scan (step 5).