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1 Exercise 1  Given the following tables: employee (person_name, street, city)‏ works (person_name, company_name, salary)‏ company (company_name, city)‏

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Presentation on theme: "1 Exercise 1  Given the following tables: employee (person_name, street, city)‏ works (person_name, company_name, salary)‏ company (company_name, city)‏"— Presentation transcript:

1 1 Exercise 1  Given the following tables: employee (person_name, street, city)‏ works (person_name, company_name, salary)‏ company (company_name, city)‏ manages (person_name, manager_name)‏

2 2  Find the name of employees who earn more than $10,000 and live in Hong Kong. select w.person_name from works as w where w.salary > and w.person_name in (select e.person_name from employee as e where e.city = “Hong Kong”)‏  Alternative solutions select w.person_name from works as w, employee as e where w.salary > and e.city = “Hong Kong” and w.person_name = e.person_name employee (person_name, street, city)‏ works (person_name, company_name, alary)‏ company (company_name, city)‏ manages (person_name, manager_name)‏

3 3  Find the name of the employees who are not managers. (select person_name from employee)‏ except (select manager_name from manages)‏ employee (person_name, street, city)‏ works (person_name, company_name, alary)‏ company (company_name, city)‏ manages (person_name, manager_name)‏

4 4  Alternative solutions select person_name from employee where not exists (select * from manages where employee.person_name = manages.manager_name)‏ select person_name from employee where person_name not in (select manager_name from manages)‏ employee (person_name, street, city)‏ works (person_name, company_name, alary)‏ company (company_name, city)‏ manages (person_name, manager_name)‏

5 5 RA SQL  Given the following tables: employee (person_name, street, city)‏ works (person_name, company_name, salary)‏ company (company_name, city)‏ manages (person_name, manager_name)‏  Find the names of all persons who work for “First Bank Corporation” and live in the city where the company is located.

6 6 select E.person_name from employee as E, works as W, company as C where E.person_name = W.person_name and W.company_name = C.company_name and C.company_name = “First Bank Corporation” and E.city = C.city employee (person_name, street, city)‏ works (person_name, company_name, alary)‏ company (company_name, city)‏ manages (person_name, manager_name)‏

7 7  Find the names, cities of employees who work for exactly ONE company select e.person_name, e.city from employee as e where unique (select * from works as w where w.person_name = e.person_name) employee (person_name, street, city)‏ works (person_name, company_name, salary)‏ company (company_name, city)‏ manages (person_naame, manager_name)‏

8 8  Find the names of all employees who earn more than SOME employee of Small Bank Corporation. select w1.person_name from works as w1 where w1.salary > some (select w2.salary from works as w2 where w2.company_name = “Small Bank Corporation”)‏  Alternative solution select w1.person_name from works as w1 where exists (select * from works as w2 where w2.company_name = “Small Bank Corporation” and w1.salary > w2.salary)‏ employee (person_name, street, city)‏ works (person_name, company_name, salary)‏ company (company_name, city)‏ manages (person_naame, manager_name)‏

9 9  Find the company located in Hong Kong that has the largest number of employees select temp.company_name from (select w.company_name, count(distinct w.person_name) as cnt from works as w, company as c where w.company_name = c.company_name and c.city = “Hong Kong” group by w.company_name) as temp where temp.cnt in (select max (cnt)‏ from temp)‏ employee (person_name, street, city)‏ works (person_name, company_name, salary)‏ company (company_name, city)‏ manages (person_naame, manager_name)‏ Can also be ‘=’

10 10  Find all companies located in Hong Kong and have total payroll less than 100,000 select company.company_name from works, company where works.company_name = company.company_name and company.city = “Hong Kong” group by company.company_name having sum(works.salary) < 100,000 employee (person_name, street, city)‏ works (person_name, company_name, salary)‏ company (company_name, city)‏ manages (person_naame, manager_name)‏

11 11  Question: Consider the following schemas. CUST (cust-id, name), and WITHDRAW (w-id, cust-id, acc-id, date, amount)  Write an SQL query to retrieve all the names of the customers who have withdrawn more than 1k dollars in a single withdrawal. If a customer made several such withdrawals, her/his name should be reported only once.

12 12  Answer: Consider the following schemas. CUST (cust-id, name), and WITHDRAW (w-id, cust-id, acc-id, date, amount)  Write an SQL query to retrieve all the names of the customers who have withdrawn more than 1k dollars in a single withdrawal. If a customer made several such withdrawals, her/his name should be reported only once. select distinct name from CUST as T1, WITHDRAW as T2 where T1.cust-id = T2.cust-id and T2.amount > 1k

13 13  Question: Consider the following schemas. CUST (cust-id, name), and WITHDRAW (w-id, cust-id, acc-id, date, amount)  Sometimes there may be a “shared” account, namely, an account with multiple owners.  Write an SQL query to return the acc-id of all the shared accounts. You may assume that all the owners of a shared account have made withdrawals from the account.

14 14  Answer: Consider the following schemas. CUST (cust-id, name), and WITHDRAW (w-id, cust-id, acc-id, date, amount)  Sometimes there may be a “shared” account, namely, an account (acc-id) with multiple owners (cust-id).  Write an SQL query to return the acc-id of all the shared accounts. You may assume that all the owners of a shared account have made withdrawals from the account. select T1.acc-id from WITHDRAW as T1, WITHDRAW as T2 where T1.cust-id <> T2.cust-id and T1.acc-id = T2.acc-id

15 15  Question: Consider the following schemas. CUST (cust-id, name), and WITHDRAW (w-id, cust-id, acc-id, date, amount)  Let us use the name “interesting account” to refer to the account from which the withdrawal with smallest amount was made.  Retrieve the acc-id of accounts from which withdrawals have been made, except the interesting account.

16 16  Answer: Consider the following schemas. CUST (cust-id, name), and WITHDRAW (w-id, cust-id, acc-id, date, amount)  Let us use the name “interesting account” to refer to the account from which the withdrawal with smallest amount was made.  Retrieve the acc-id of accounts from which withdrawals have been made, except the interesting account. select distinct acc-id from WITHDRAW where acc-id not in (select acc-id from WITHDRAW where amount = (select min (amount) from WITHDRAW))

17 17  Consider table: deposit (dep-id, acc-id, cust-id, amount). We want to retrieve the cust-id of the customers who deposited into two accounts with acc-id ‘A1’ and ‘A2’, respectively.  Write an SQL query with intersect. (select distinct cust-id from deposit where acc-id = ‘A1’) intersect (select distinct cust-id from deposit where acc-id = ‘A2’)  Write a nested SQL query without intersect. select distinct cust-id from deposit where acc-id = ‘A1’ and cust-id in (select cust-id from deposit where acc-id = ‘A2’) dep-idacc-idcust-idamount A112K A111K A211K A223K A332K A325K

18 18  Again consider table: deposit (dep-id, acc-id, cust-id, amount). We want to retrieve the cust-id of the customers who deposited into two accounts with acc-id ‘A1’ and ‘A2’, respectively.  Write an SQL query that contains only one select. select distinct T1.cust-id from deposit as T1, deposit as T2 where T1.cust-id = T2.cust-id and T1.acc-id = ‘A1’ and T2.acc-id = ‘A2’ dep-idacc-idcust-idamount A112K A111K A211K A223K A332K A325K

19 19  Find the ids of the accounts which have been deposited into by more than one customer.  Write a SQL query without group by : select D1.acc-id from deposit as D1, deposit as D2 where D1.cust-id <> D2.cust-id and D1.acc-id = D2.acc-id dep-idacc-idcust-idamount A112K A111K A211K A223K A332K A325K

20 20  Find the ids of the accounts which have been deposited into by more than one customer.  Write a SQL query with group by : select acc-id from deposit group by acc-id having count (distinct cust-id) >= 2  If there is no distinct here, A1 will also be displayed. dep-idacc-idcust-idamount A112K A111K A211K A223K A332K A325K

21 21  Again consider table: deposit (dep-id, acc-id, cust-id, amount). We want to retrieve the cust-id of the customers who deposited into the account with acc-id = ‘A1’ or ‘A2’ but not both.  Write an SQL query that contains only one SELECT. select cust-id from deposit where acc-id = ‘A1’ or acc-id = ‘A2’ group by cust-id having count (distinct acc-id) = 1 Indispensable! dep_idacc-idcust-idamount A112K A111K A211K A223K A332K A325K

22 22  deposit (dep-id, acc-id, cust-id, amount). Retrieve the cust-id of the customer who deposited the largest number of times. select cust-id from deposit group by cust-id having count (*) >= all (select count (*) from deposit group by cust-id) dep-idacc-idcust-idamount A112K A111K A211K A223K A332K A325K

23 23  Question: As with natural join, outer joins are not compulsory operators. That is, we can implement an outer join using “conventional” SQL.  Let us verify this for left outer join.  CS-PROF (prof-id, name)  SUPERVISION (prof-id, stu-id)  Write an alternative query that returns the same information as select prof-id, name, stu-id from CS-PROF left outer join SUPERVISION on CS-PROF.prof-id = SUPERVISION.prof-id

24 24  Answer:  CS-PROF (prof-id, name)  SUPERVISION (prof-id, stu-id) select prof-id, name, stu-id from CS-PROF left outer join SUPERVISION on CS-PROF.prof-id = SUPERVISION.prof-id (select T1.prof-id, name, stu-id from CS-PROF as T1, SUPERVISION as T2 where T1.prof-id = T2.prof-id) union (select prof-id, name, NULL from CS-PROF as T1 where not exists (select * from SUPERVISION as T2 where T1.prof-id = T2.prof-id))  We can see that left outer join simplifies the query significantly.

25 25  Question: Consider MARKS(stu-id, course-id, score)  Write a query to retrieve the stu-id of every student who scored at least 80 in all the courses s/he took, but scored less than 90 in at least one course.  Your query should not contain more than 2 select.

26 26  Answer: Consider MARKS(stu-id, course-id, score).  Write a query to retrieve the stu-id of every student who scored at least 80 in all the courses s/he took, but scored less than 90 in at least one course. (select stu-id from MARKS where score < 90) except (select stu-id from MARKS where score < 80)

27 27  Answer: Consider MARKS (stu-id, course-id, score).  Write a query to retrieve the stu-id of every student who scored at least 80 in all the courses s/he took, but scored less than 90 in at least one course. select stu-id from MARKS group by stu-id having min (score) >= 80 and min (score) < 90

28 28  What will happen if some of values of score are NULL in table ?  All aggregate operations except count(*) ignore tuples with null values on the aggregated attributes.


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