CSIT5300: Advanced Database Systems

Size: px

Start display at page:

Download "CSIT5300: Advanced Database Systems"

Todd Horatio Hodge
6 years ago
Views:

1 CSIT5300: Advanced Database Systems E03: SQL Part 1 Exercises Dr. Kenneth LEUNG Department of Computer Science and Engineering The Hong Kong University of Science and Technology Hong Kong SAR, China kwtleung@cse.ust.hk CSIT5300

2 Exercise #1 Let R(A,B,C) and S(D,E,F) be two union compatible relation schemas. Convert the following algebra expressions to SQL (for simplicity, you can omit distinct): π A (R) A R σ C=12 (R) * R C=12 π A,F (R JOIN C=D S) A, F R, S C=D π A (R) - π D (S) A R except D S kwtleung@cse.ust.hk CSIT5300 2

3 Exercise #2 (Example Database Schema and Instance) Sailors (sid, sname, rating, age), Sailors sid sname rating age 22 dustin lubber rusty Reserves sid bid day /10/ /12/96 kwtleung@cse.ust.hk CSIT5300 3

4 Exercise #2 Q1 Q1: Find the names of sailors who reserved bid=103 S.sid S x R S.sname Sailors as S, Reserves as R S.sid=R.sid and R.bid=103 R.sid (sid) sname rating age (sid) bid day 22 dustin /10/96 22 dustin /12/96 31 lubber /10/96 31 lubber /12/96 58 rusty /10/96 58 rusty /12/96 kwtleung@cse.ust.hk CSIT5300 4

5 Exercise #2 Q2 Q2: Find the sid s of sailors who reserved a red or a green boat Solution #1 Solution #2 R.sid Boats as B, Reserves as R R.bid=B.bid and (B.color= red or B.color= green ) What do we get if we replace or by and in the first solution? union R.sid Boats as B, Reserves as R R.bid=B.bid and B.color= red R.sid Boats as B, Reserves as R R.bid=B.bid and B.color= green What do we get if we replace union by except in the second solution? kwtleung@cse.ust.hk CSIT5300 5

6 Exercise #2 Q3 Q3: Find the sid s of sailors who reserved a red and a green boat Solution #1 S.sid Sailors as S, Boats as B1, Reserves as R1, Boats as B2, Reserves as R2 S.sid=R1.sid and R1.bid=B1.bid and B1.color= red and S.sid=R2.sid and R2.bid=B2.bid and B2.color= green Solution #2 intersect Key field! S.sid Sailors as S, Boats as B, Reserves as R S.sid=R.sid and R.bid=B.bid and B.color= red S.sid Sailors as S, Boats as B, Reserves as R S.sid=R.sid and R.bid=B.bid and B.color= green What if instead of the sid we want the sname? Would the queries be correct if we replace S.sid with S.sname in? kwtleung@cse.ust.hk CSIT5300 6

7 Exercise #2 Q4 Q4: Find the names of sailors who have not reserved bid=103 S.sname Sailors as S S.sid not in ( R.sid Reserves as R R.bid=103) kwtleung@cse.ust.hk CSIT5300 7

8 Exercise #2 Q5 Q5: Find the names of sailors who have reserved a red boat (you must use in) S.sname Sailors as S S.sid in ( R.sid Reserves as R R.bid in ( B.bid Boats as B B.color=red) What if we replace the first in with not in? What if we replace the second in with not in? What if we replace both in with not in? kwtleung@cse.ust.hk CSIT5300 8

9 Exercise #2 Q6 Q6: Find the names of sailors who have reserved bid=103 (you must use exists) S.sname Sailors as S exists ( * Reserves as R R.bid=103 and S.sid=R.sid) What if we replace exists with not exists? What if we replace exists with unique? kwtleung@cse.ust.hk CSIT5300 9

10 Exercise #2 Q7 Q7: Find the record of the sailor with the highest rating * Sailors as S S.rating >= all ( S2.rating Sailors as S2) What if we replace all with some? kwtleung@cse.ust.hk CSIT

11 Exercise #2 Q8 Q8: Find the names of sailors who reserved all boats S.sname Sailors as S not exists (( B.bid Boats as B) except ( R.bid Reserves as R R.sid=S.sid)) kwtleung@cse.ust.hk CSIT

Database Management Systems. Chapter 5

Database Management Systems. Chapter 5 Database Management Systems Chapter 5 SQL: Queries, Constraints, Triggers Example Instances We will use these instances of the Sailors and Reserves relations in our examples. If the key for the Reserves