Intermediate SQL ( )

Transcription

1 CSL 451 Introduction to Database Systems Intermediate SQL ( ) Department of Computer Science and Engineering Indian Institute of Technology Ropar Narayanan (CK) Chatapuram Krishnan!

2 Summary Join Expressions Natural Join Join using on outer joins left right full difference between predicate appearing in on and where clause inner joins Views virtual relations create view materialized views Update of a view updatable views with check option Transactions commit (work) rollback (work) atomicity Integrity constraints prevent data inconsistency constraints on a single relation not null unique check referential integrity cascade transactions deferrable 2!

3 4.1.a Display the list of all instructors, showing their ID, name, and the number of sections that they have taught. Make sure to show the number of sections as 0 for instructors who have not taught any section. Your query should use an outer join, and should not use scalar sub-queries. 3!

4 4.1.b Write the previous query using a scalar subquery, but without the outer join. 4!

5 4.1.c Display the list of all course sections offered in Spring 2010, along with the names of the instructors teaching the section. If a section has more than one instructor, it should appear as many times in the result as it has instructors. If it does not have any instructor, it should still appear in the result with the instructor name set to -. 5!

6 4.1.d Display the list of all departments, with the total number of instructors in each department, without using scalar subqueries. Make sure to correctly handle departments with no instructors. 6!

7 4.2.a Rewrite the query without using the outer join expression select * from student natural left outer join takes 7!

8 4.2.a Rewrite the query without using the outer join expression select * from student natural full outer join takes 8!

9 4.3.a Suppose we have three relations r(a, B), s(b,c) and t(b,d), with all attributes declared as not null. Consider the expression (r natural left outer join s) natural left outer join t Give instances of relations r, s, and t such that in the result of the expression attribute C has a null value, but attribute D has a non-null value. 9!

10 4.3.b Suppose we have three relations r(a, B), s(b,c) and t(b,d), with all attributes declared as not null. Consider the expression r natural left outer join (s natural left outer join t) Is the pattern with C null and D not null possible in the result of this expression? Explain why or why not? 10!

11 4.12 Find employees with no manager. Note that an employee may simply have no manger listed or may have a null manager. Write the query using outer join employee (employee_name, street, city) works (employee_name, company_name, salary) company (company_name, city) manages (employee_name, manager_name) 11!

12 4.12 Find employees with no manager. Note that an employee may simply have no manger listed or may have a null manager. Write the query without using outer join employee (employee_name, street, city) works (employee_name, company_name, salary) company (company_name, city) manages (employee_name, manager_name) 12!

13 4.12 Under what circumstances would the query select * from student natural full outer join takes natural full outer join course include tuples with null values for the title attribute? 13!

14 4.4.b When creating test databases, it is important to create tuples in referenced relations that do not have any matching tuple in the referencing relation, for each foreign key. Explain why, using an example query on the university database. 14!

15 4.4.c When creating test databases, it is important to create tuples with null values for foreign key attributes, provided the attribute is nullable (SQL allows foreign key attributes to take on null values, as long as they are not part of the primary key, and have not been declared as not null). Explain why, using an example query on the university database. movie(mid, title, year, director) rating(mid, rid, stars, ratingdate) reviewer(rid, name) 15!

16 4.5 Show how to define the view student_grades (ID, GPA) giving the grade point average of each student. Make sure your view definition correctly handles the case of null values for the grade attribute of the takes relation. 16!

17 4.14 show how to define a view tot_credits (year, num_credits), giving the total number of credits taken by students in each year. 17!

18 EN 5.8.a Write a view that has the department name, manager name and manager salary for every department 18!

19 EN 5.8.b Write a view that has the employee name, supervisor name and employee salary for every employee working in the Research Department 19!

20 EN 5.9.d Consider the following view Create view dept_summary(d, c, total_s, average_s) as (select dno, count(*), sum(salary), avg(salary) from employee group by dno) State whether the following update would be allowed on the view. update dept_summary set d=3 where d=4; 20!

21 EN 5.9.e Consider the following view Create view dept_summary(d, c, total_s, average_s) as (select dno, count(*), sum(salary), avg(salary) from employee group by dno) State whether the following update would be allowed on the view. delete from dept_summary where c > 4; 21!

22 4.8.a Expect the constraint an instructor cannot teach sections in two different classrooms in a semester in the same time slot to hold. Write an SQL query that returns all (instructor, section) combinations that violate this constraint. 22!

23 4.9 SQL allows a foreign-key dependency to refer to the same relation, as in the following example: create table manager (employee_name manager_name varchar(20) not null, varchar(20) not null, primary key employee_name, foreign key (manager_name) references manager on delete cascade) Here, employee_name is a key to the table manager, meaning that each employee has at most one manager. The foreign-key clause requires that every manager also be an employee. Explain exactly what happens when a tuple in the relation manager is deleted. 23!

24 4.16.a Referential-integrity constraints as defined in this chapter involve exactly two relations. Consider a database that includes the relations salaried worker (name, office, phone, salary) hourly worker (name, hourly wage) address (name, street, city) Suppose that we wish to require that every name that appears in address appears in either salaried worker or hourly worker, but not necessarily in both. Propose a syntax for expressing such constraints. 24!

25 4.16.b Referential-integrity constraints as defined in this chapter involve exactly two relations. Consider a database that includes the relations salaried worker (name, office, phone, salary) hourly worker (name, hourly wage) address (name, street, city) Suppose that we wish to require that every name that appears in address appears in either salaried worker or hourly worker, but not necessarily in both. Discuss the actions that the system must take to enforce a constraint of this form. 25!

26 Consider the following two queries. Will they produce the same result? If so when? select distinct director from movie where title not in (select title from movie natural join rating natural join reviewer where reviewer like %Cameron% ); select distinct director from movie where title in (select title from movie natural join rating natural join reviewer where reviewer not like %Cameron% ); 26!