CMPT 258 Database SystemsSQL: Queries, Constraints, Triggers(Chapter 5) Part IIhome.manhattan.edu/~tina.tian

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3

Agenda

•Introduction•Basic SQL Query•Union, Intersection and Except•Nested Queries•Aggregate Operations•Complex Integrity Constraints in SQL•Triggers

Examples

sid sname rating age

22 dustin 7 45.0

31 lubber 8 55.5 58 rusty 10 35.0

bid bname color101 Interlake Blue102 Interlake Red103 Clipper Green104 Marine Red

sid bid day

22 101 10/10/9658 103 11/12/96

Reserves

Sailors

Boats

4

•Union (supported in MySQL)•Intersect•Except/Minus

5

Find sid’s of sailors who’ve reserved a red or a green boat

SELECT R.sidFROM Boats B, Reserves RWHERE R.bid=B.bid AND B.color=‘red’UNIONSELECT R.sidFROM Boats B, Reserves RWHERE R.bid=B.bid AND B.color=‘green’

supported in MySQL

Find sid’s of sailors who’ve reserved a red and a green boat

SELECT R.sidFROM Boats B, Reserves RWHERE R.bid=B.bid AND B.color=‘red’INTERSECTSELECT R.sidFROM Boats B, Reserves RWHERE R.bid=B.bid AND B.color=‘green’

Find sid’s of sailors who’ve reserved a red boat but not a green boat

SELECT R.sidFROM Boats B, Reserves RWHERE R.bid=B.bid AND B.color=‘red’EXCEPTSELECT R.sidFROM Boats B, Reserves RWHERE R.bid=B.bid AND B.color=‘green’

Example

SELECT S.snameFROM Sailors S, Reserves RWHERE S.sid = R.sid AND R.bid=103

Find names of sailors who’ve reserved boat #103:

sid bid day

22 101 10/10/9658 103 11/12/96

sid sname rating age

22 dustin 7 45.0

31 lubber 8 55.5 58 rusty 10 35.0

ReservesSailors

Nested Queries

• Understand semantics of nested queries ▫For each Sailors tuple, check

the qualification by computing the subquery.

SELECT snameFROM Sailors WHERE sid IN (SELECT sid FROM Reserves WHERE bid=103)

Find names of sailors who’ve reserved boat #103:

sid bid day

22 101 10/10/9658 103 11/12/96

sid sname rating age

22 dustin 7 45.0

31 lubber 8 55.5 58 rusty 10 35.0

Nested QueriesFind names of sailors who’ve NOT reserved boat #103:

SELECT S.snameFROM Sailors S, Reserves RWHERE S.sid = R.sid AND R.bid<>103

sid bid day

22 101 10/10/9658 103 11/12/96

sid sname rating age

22 dustin 7 45.0

31 lubber 8 55.5 58 rusty 10 35.0

ReservesSailors

Is this correct?

Nested Queries

“Find names of sailors whose ids do not appear amongthe ids that reserved boat #103”is different with“Find names of sailors who have reserved a boat that is not 103”

Find names of sailors who’ve NOT reserved boat #103:

sid bid day

22 101 10/10/9658 103 11/12/96

sid sname rating age

22 dustin 7 45.0

31 lubber 8 55.5 58 rusty 10 35.0

ReservesSailors

Nested Queries

SELECT snameFROM Sailors WHERE sid NOT IN (SELECT sid FROM Reserves WHERE bid=103)

Find names of sailors who’ve NOT reserved boat #103:

A very powerful feature of SQL: a WHERE clause can itself contain an SQL query!

sid bid day

22 101 10/10/9658 103 11/12/96

sid sname rating age

22 dustin 7 45.0

31 lubber 8 55.5 58 rusty 10 35.0

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•Q: Find the sids of sailors who have reserved a red boat

SELECT R.sidFROM Reserves R, Boats BWHERE R.bid = B.bid and B.color=‘red’

sid bid day

22 101 10/10/9658 103 11/12/96

Reserves

bid bname color101 Interlake Blue102 Interlake Red103 Clipper Green104 Marine Red

Boats

Rewrite the queryusing IN?

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•Q: Find the names of sailors who have reserved a red boat

16

•Q: Find the names of sailors who have not reserved a red boat

Rewriting INTERSECT Queries Using INQ: Find sid’s of sailors who’ve reserved both a red and a green boat:

sid bid day

22 101 10/10/9658 103 11/12/96

Reserves

bid bname color101 Interlake Blue102 Interlake Red103 Clipper Green104 Marine Red

Boats

Rewriting EXCEPT Queries

Q: Find sid’s of sailors who’ve reserved a red but not a green boat:

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Find the names of sailors who’ve reserved a red and a green boat

• Is this query correct? Why

SELECT S.snameFROM Sailors S, Reserves R, Boats B WHERE S.sid=R.sid AND R.bid=B.bid AND B.color=‘red’INTERSECTSELECT S.snameFROM Sailors S, Boats B, Reserves RWHERE S.sid=R.sid AND R.bid=B.bid AND B.color=‘green’

20

Find the names of sailors who’ve reserved a red and a green boat

Set-Comparison Operators•Also available: op ANY, op ALL

▫OP is one of , <>•Q: Find sailors whose rating is equal to that

of some sailor called Horatio:

• Can you rewrite the query without using set-comparison operators?

, , , , ,

SELECT *FROM Sailors WHERE rating = ANY (SELECT rating FROM Sailors WHERE sname=‘Horatio’)

Set-Comparison Operators

•IN is equivalent to =ANY•NOT IN is equivalent to <>ANY

SELECT *FROM Sailors WHERE rating <> ANY (SELECT rating FROM Sailors WHERE sname=‘Horatio’)

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Set-Comparison Operators•Q: Find sailors whose rating is better than

every sailor called Horatio.SELECT *FROM Sailors WHERE rating > ALL (SELECT rating FROM Sailors WHERE sname=‘Horatio’)

24

Set-Comparison Operators•Q: Find the sailors with the highest

rating.

Summary

•ANY•ALL•>,>=,<,<= [ANY/ALL]•IN is equivalent to =ANY•NOT IN is equivalent to <>ANY

25

Nested Queries with Correlation

SELECT S.snameFROM Sailors SWHERE EXISTS (SELECT * FROM Reserves R WHERE R.bid=103 AND S.sid=R.sid)

Q: Find names of sailors who’ve reserved boat #103:

sid bid day

22 101 10/10/9658 103 11/12/96

sid sname rating age

22 dustin 7 45.0

31 lubber 8 55.5 58 rusty 10 35.0

ReservesSailors

Nested Queries with Correlation

SELECT S.snameFROM Sailors SWHERE EXISTS (SELECT * FROM Reserves R WHERE R.bid=103 AND S.sid=R.sid)

Q: Find names of sailors who’ve reserved boat #103:

SELECT S.snameFROM Sailors SWHERE S.sid IN (SELECT R.sid FROM Reserves R WHERE R.bid=103

SELECT S.snameFROM Sailors S, Reserves RWHERE S.sid=R.sid and R.bid=103

Nested Queries with Correlation

• EXISTS is another set comparison operator, like IN.

• NOT EXISTS

SELECT S.snameFROM Sailors SWHERE NOT EXISTS (SELECT * FROM Reserves R WHERE R.bid=103 AND S.sid=R.sid)

Q: Find names of sailors who’ve not reserved boat #103:

sid bid day

22 101 10/10/9658 103 11/12/96

sid sname rating age

22 dustin 7 45.0

31 lubber 8 55.5 58 rusty 10 35.0

Reserves Sailors

Division in SQL

Find names of sailors thatthere is no boat that has not been reserved by this sailor

Q: Find names of sailors who’ve reserved all boats.

sid bid day

22 101 10/10/9658 103 11/12/96

sid sname rating age

22 dustin 7 45.0

31 lubber 8 55.558 rusty 10 35.0Reserves

Sailors

bid bname color101 Interlake Blue102 Interlake Red103 Clipper Green104 Marine Red

Boats

Division in SQL

SELECT S.snameFROM Sailors SWHERE NOT EXISTS

(SELECT bidFROM BoatsWHERE bid NOT IN

(SELECT R.bidFROM Reserves RWHERE R.sid=S.sid))

For each sailor we check that there is no boat that has not been reserved by this sailor

Q: Find names of sailors who’ve reserved all boats.

•IN•NOT IN•EXISTS•NOT EXISTS

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Readings

•Chapter 5