international computer institute, izmir, turkey sql asst.prof.dr.İlker kocabaş ubİ502 at ikocabas

International Computer Institute, Izmir, TurkeyInternational Computer Institute, Izmir, Turkey

SQLSQL

Asst.Prof.Dr.İlker Kocabaş

UBİ502 at http://ube.ege.edu.tr/~ikocabas

©Silberschatz, Korth and Sudarshan

Modifications & additions by Cengiz Güngör5.2 of 48

UBI 502

Database Management Systems

OverviewOverview

Joins: types and conditions

Example 1: our languages relational algebra

tuple relational calculus

domain relational calculus

SQL

Examples 2, 3 joins, aggregates, MySQL

Join tricks



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Schema Diagram for the Banking EnterpriseSchema Diagram for the Banking Enterprise



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JoinsJoins

Join types: Inner join

Left outer join

Right outer join

Full outer join

Join conditions: Natural

On <predicate>

Using (A1, …, An)



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The The loan loan and and borrowerborrower Relations Relations



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loanloan INNER JOIN INNER JOIN borrowerborrowerON ON loan.loan-number = borrower.loan-numberloan.loan-number = borrower.loan-number



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loan loan LEFT OUTER JOIN LEFT OUTER JOIN borrowerborrowerUSINGUSING (loan-number)loan-number)



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Join ConditionsJoin Conditions

a INNER JOIN b USING (c1, ..., cn)

SELECT * FROM loan INNER JOIN borrower USING (loan_number);+-------------+-------------+--------+---------------+-------------+| loan_number | branch_name | amount | customer_name | loan_number |+-------------+-------------+--------+---------------+-------------+| L-16 | Perryridge | 1300 | Adams | L-16 || L-93 | Mianus | 500 | Curry | L-93 |...| L-17 | Downtown | 1000 | Williams | L-17 |+-------------+-------------+--------+---------------+-------------+

Equivalent:

a INNER JOIN b ON (a.c1 = b.c1, …, a.cn = b.cn)



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Join ConditionsJoin Conditions

Suppose (c1, …, cn) is a complete list of attributes common to A and B

Then:a INNER JOIN b USING (c1, …, cn)

is equivalent to:a NATURAL JOIN b

E.g. since there is only one common attribute between loan and borrower, the following queries give the same result:SELECT * FROM loan INNER JOIN borrower USING (loan_number);

SELECT * FROM loan NATURAL JOIN borrower;



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Example 1: Our languagesExample 1: Our languages

Query: What branches are in Brooklyn?

branch-name (branch-city = “Brooklyn” (branch))

{t | s branch (t[branch-name] = s[branch-name] s [branch-city] = “Brooklyn”)}

{ n | c, a ( n, c, a branch c = “Brooklyn”)}

SELECT branch-name FROM branchWHERE branch_city = “Brooklyn”



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Example 2Example 2

Who has a loan with a greater value than every loan at Perryridge branch?

t1 ← mp(max) ( g max(amount) (branch-name = “Perryridge” (loan)))

(customer-name(loan-number(amount > t1.max (loan)) ⋈ borrower)



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Example 2 (cont)Example 2 (cont)

branch-name = “Perryridge” (loan)

mysql> SELECT * FROM loan

-> WHERE branch_name = "Perryridge";

+-------------+-------------+--------+

| loan_number | branch_name | amount |

+-------------+-------------+--------+

| L-15 | Perryridge | 1500 |

| L-16 | Perryridge | 1300 |

+-------------+-------------+--------+



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g max(amount) (branch-name = “Perryridge” (loan))

mysql> SELECT MAX(amount) FROM loan


+-------------+

| max(amount) |

+-------------+

| 1500 |

+-------------+



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mp(max) ( g max(amount) (branch-name = “Perryridge” (loan)))

mysql> SELECT MAX(amount) AS max FROM loan


+------+

| max |

+------+

| 1500 |

+------+



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t1 ← mp(max) ( g max(amount) (branch-name = “Perryridge” (loan)))

mysql> CREATE TEMPORARY TABLE t1

-> SELECT MAX(amount) AS max FROM loan




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amount > t1.max (loan)

mysql> SELECT * FROM loan, t1

-> WHERE amount > t1.max;

+-------------+-------------+--------+------+

| loan_number | branch_name | amount | max |

+-------------+-------------+--------+------+

| L-23 | Redwood | 2000 | 1500 |

| L-20 | North Town | 7500 | 1500 |

+-------------+-------------+--------+------+



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(amount (amount > t1.max (loan))

mysql> SELECT amount FROM loan, t1


+--------+

| amount |

+--------+

| 2000 |

| 7500 |

+--------+



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Example 3Example 3

Query: What is the average loan amount held by customers in each city?

branch-city g avg(amount) (loan ⋈ branch)



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mysql> select * -> from loan natural join branch;

+-------------+-------------+--------+-------------+-------------+---------+| loan_number | branch_name | amount | branch_name | branch_city | assets |+-------------+-------------+--------+-------------+-------------+---------+| L-17 | Downtown | 1000 | Downtown | Brooklyn | 900000 || L-23 | Redwood | 2000 | Redwood | Palo Alto | 2100000 || L-15 | Perryridge | 1500 | Perryridge | Horseneck | 1700000 || L-14 | Downtown | 1500 | Downtown | Brooklyn | 900000 || L-93 | Mianus | 500 | Mianus | Horseneck | 400200 || L-11 | Round Hill | 900 | Round Hill | Horseneck | 8000000 || L-16 | Perryridge | 1300 | Perryridge | Horseneck | 1700000 || L-20 | North Town | 7500 | North Town | Rye | 3700000 || L-21 | Central | 570 | Central | Rye | 400280 |+-------------+-------------+--------+-------------+-------------+---------+

Would like to see just the branch_name and branch_city columns



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mysql> select branch_city, amount -> from loan natural join branch;

+-------------+--------+| branch_city | amount |+-------------+--------+| Brooklyn | 1000 || Palo Alto | 2000 || Horseneck | 1500 || Brooklyn | 1500 || Horseneck | 500 || Horseneck | 900 || Horseneck | 1300 || Rye | 7500 || Rye | 570 |+-------------+--------+

Would like to see this table sorted by branch_city



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mysql> select branch_city, amount -> from loan natural join branch -> order by branch_city;+-------------+--------+| branch_city | amount |+-------------+--------+| Brooklyn | 1000 || Brooklyn | 1500 || Horseneck | 1300 || Horseneck | 1500 || Horseneck | 500 || Horseneck | 900 || Palo Alto | 2000 || Rye | 7500 || Rye | 570 |+-------------+--------+

Next: compute average for each group



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mysql> select branch_city, avg(amount)

-> from loan natural join branch

-> group by branch_city;

+-------------+-------------+

| branch_city | avg(amount) |

+-------------+-------------+

| Brooklyn | 1250.0000 |

| Horseneck | 1050.0000 |

| Palo Alto | 2000.0000 |

| Rye | 4035.0000 |

+-------------+-------------+

Suppose we wanted to impose a constraint on the result – use a HAVING clause



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mysql> select branch_city as city, avg(amount) as average

-> from loan natural join branch

-> group by branch_city

-> having (avg(amount) > 1500);

+-----------+-----------+

| city | average |

+-----------+-----------+

| Palo Alto | 2000.0000 |

| Rye | 4035.0000 |

+-----------+-----------+

Note: we also renamed the columns



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Join tricksJoin tricks

Restrict a to just those rows compatible with b SELECT DISTINCT a.* FROM a NATURAL JOIN b;

E.g. list tuples from the borrower table only for those borrowers who are depositors: SELECT DISTINCT borrower.*

FROM borrower NATURAL JOIN depositor;



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Join tricks (cont)Join tricks (cont)

Compute set difference without using EXCEPT(MySQL 3.23 doesn’t have set operations)i.e.remove from a those tuples compatible with b SELECT DISTINCT a.* FROM a NATURAL LEFT OUTER JOIN b

WHERE b.x is NULL

E.g. list those tuples from the borrower table only for those borrowers who are not depositors: SELECT DISTINCT borrower.*

FROM borrower NATURAL LEFT OUTER JOIN depositorWHERE depositor.customer_name is NULLS



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ReviewReview

A NATURAL JOIN uses common column headings, and it is not possible to attach an ON or USING clause

An INNER JOIN results in a table where each tuple is a combination of information from both argument tables

An OUTER JOIN is an INNER JOIN padded with additional tuples

The ON clause lists common attributes which must be equal on both sides of the join

The USING clause permits us to enforce equality between attributes having different names, e.g. ON a.x = b.y

It also permits us to use inequalities, e.g. ON a.x > b.y



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PS: Theta JoinPS: Theta Join

A ⋈C B ≝ C (A ⋈ B)

For notational convenience, we permit ourselves to write a select condition on the join operator

This is called “theta join” because the condition is sometimes represented as a theta subscript:

⋈θ



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READINGREADING

MySQL manual chapter 3: Tutorial Introduction

http://www.mysql.com/documentation/mysql/bychapter/manual_Tutorial.html

international computer institute, izmir, turkey sql asst.prof.dr.İlker kocabaş ubİ502 at ikocabas

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