10/05/2015 Introduction to Databases 1 F27DB Introduction to Database Systems More SQL Helen Hastie...

18/04/23 Introduction to Databases 1

F27DB Introduction to Database Systems More SQL

Helen [email protected]

Room: EMB244Material available on Vision (modified from slides

by Monica Farrow)


Recap

• SQL already introduced in Helen’s lectures 1 & 2, and Brian’s lecture 5 & 6

• Here are some more examples on Views, Aggregate functions and updates

• Using the Spy tables• With additional interest rate table for different

types of account


The tables now

SpycodeName firstNamedateOfBirthgendermarkamountDuespyMaster bankAccount

SpyMastermCodeNamebankAccountcontact

SpyAccountaccountNumberIncomeExpenditureatype

SpySkillListskillCodeskillName

1..*

1

1

1..*

1

1

skilled at

has

manages

1

1

SpyWithSkillspyCodeskillCode

1

0..*

practisedby

Bold : primary keyItalic : foreign keyBoth : both

has

Now the relationships are also shown by foreign keys

NB Many to many relationships need an extra ‘linking’ table

SpyAccRatesaccTyperate

1

1..*


Spy

code Name

first Name

lastName dateOfBirthgender

markamount

Duespy

Masterbank

Account

007 James Bond 12 December 1972

M Mole on chin 5050 Q 23456

bud Fanny Charleston 31 July 1983 F scar on cheek 25.67 Q 34567

freddie John Smith 05 September 1954

M one finger missing

312.5 M 45678

Spy DBSpyMaster

mCodeName

bankAccount contact

M 12345 Drop 5

P 56789 PO Box 23

Q 13579 Jimmie's

SpyAccount

account Number

income

expenditure atype

12345 0 0 savings

13579 23567 1345.89 current

23456 2000 1345 savings

34567 345 56.34 savings

45678 3579.57 5280.45 current

56789 12678 10345 current

SpySkillList

skillCode skillName

1 top shot

2 skilled with a knife

3 fast runner

4 quick thinker

5 can pilot a helicopter

SpyWithSkill

spyCode

skillCode

007 1

007 4

bud 2

bud 3

bud 4

freddie 4

freddie 5

SpyAccRates

accType rate

current 0.015

savings 0.02


Extra SQL needed

• Create new tableCREATE TABLE SpyAccRates (accType VARCHAR(10) PRIMARY KEY, rate DECIMAL( 6,3));

• Insert 2 recordsINSERT INTO SpyAccRates VALUES ('current', 0.015);INSERT INTO SpyAccRates VALUES ('savings', 0.02);

• Add new column to SpyAccount table• ALTER TABLE SpyAccount add atype VARCHAR (10);• (ought to add foreign key constraint too)

• Rather randomly allocate types to accountsUPDATE SpyAccount SET atype = 'current'; UPDATE SpyAccount SET atype = 'savings' WHERE income < 400;


Reminder – SQL query joining 2 tables

• Find the code name and contact point of SpyMasters with 0 income• SELECT mCodeName, bankAccount, income

FROM SpyMaster, SpyAccountWHERE bankAccount = accountNumberAND income = 0;

mCodename

bankAccount

Income

M 12345 0


Calculations

• Find the balance of each bank account, renaming the result of the calculation

SELECT accountNumber, income – expenditure AS ‘balance’FROM SpyAccount;

+---------------+----------+| accountNumber | balance |+---------------+----------+| 12345 | 0.00 | | 13579 | 22221.11 | | 23456 | 655.00 | | 34567 | 288.66 | | 45678 | -1700.88 | | 56789 | 2333.00 | +---------------+----------+


Count

• Count the male spies• SELECT count(*) FROM Spy

WHERE gender = ‘M’;

• Count the spies who are quick thinkers• SELECT count(*)

FROM SpyWithSkill W, SpySkills LWHERE W.skillCode = L.skillCodeAND L.skillName = ‘quick thinker’;

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

| COUNT(*) |

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

| 4 |

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

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

| COUNT(*) |

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

| 2 |

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


Sum

• Find the total amount due to all spiesSELECT sum(amountDue) FROM Spy;

+----------------+| sum(amountDue) |+----------------+| 338.17 | +----------------+


Sum and grouping

• Display the amounts due to male and female spies

SELECT gender, sum(amountDue)

FROM Spy

GROUP BY gender;• Whatever you are grouping by, must appear in

the SELECT line as well as the GROUP BY line

+--------+----------------+| gender | sum(amountDue) |+--------+----------------+| F | 25.67 | | M | 312.50 | +--------+----------------+


Income by type

• Display the total income of all account holders, grouped according to their type of accountSELECT atype, sum(income)

FROM SpyAccount

GROUP BY atype

+---------+-------------+| atype | sum(income) |+---------+-------------+| current | 39824.57 | | savings | 2345.00 | +---------+-------------+


Low income by type

• Limit the enquiry to those accounts with under 4000 in incomeSELECT atype, sum(income)

FROM SpyAccount

WHERE income < 4000

GROUP BY atype

+---------+-------------+| atype | sum(income) |+---------+-------------+| current | 3579.57 | | savings | 2345.00 | +---------+-------------+


Calculations with update

• Increase the income column for each account by 10• UPDATE SpyAccount

SET income = income + 10;

+---------------+----------+-------------+---------+| accountNumber | income | expenditure | atype |+---------------+----------+-------------+---------+| 12345 | 10.00 | 0.00 | savings | | 13579 | 23577.00 | 1345.89 | current | | 23456 | 2010.00 | 1345.00 | savings | | 34567 | 355.00 | 56.34 | savings | | 45678 | 3589.57 | 5280.45 | current | | 56789 | 12688.00 | 10345.00 | current | +---------------+----------+-------------+---------+


Calculations

• Calculate the interest due to each spy, by multiplying the income in the SpyAccount table by the rate in the SpyAccRate table.• Also rename output column for nice output

SELECT A.accountNumber, A.income * R.rate as interest FROM SpyAccount A, SpyAccRates RWHERE A.atype = R.accType;

+---------------+-----------+| accountNumber | interest |+---------------+-----------+| 12345 | 0.20000 | | 13579 | 353.65500 | | 23456 | 40.20000 | | 34567 | 7.10000 | | 45678 | 53.84355 | | 56789 | 190.32000 | +---------------+-----------+


Calculate increased income

• Calculate each spy’s new income, by adding in the interest SELECT A.accountNumber, A.income + A.income * R.rate as newIncomeFROM SpyAccount A, SpyAccRates RWHERE A.atype = R.accType;

+---------------+-------------+| accountNumber | newIncome |+---------------+-------------+| 12345 | 10.20000 | | 13579 | 23930.65500 | | 23456 | 2050.20000 | | 34567 | 362.10000 | | 45678 | 3643.41355 | | 56789 | 12878.32000 | +---------------+-------------+


Update data in one table with data from another

• There are 2 ways of doing this.• 1) Provide all the tablenames involved straight

awayUPDATE SpyAccount A, SpyAccRates RSET A.income = A.income + A.income * R.rateWHERE A.atype = R.accType;

+---------------+----------+-------------+---------+| accountNumber | income | expenditure | atype |+---------------+----------+-------------+---------+| 12345 | 10.20 | 0.00 | savings | | 13579 | 23930.66 | 1345.89 | current | | 23456 | 2050.20 | 1345.00 | savings | | 34567 | 362.10 | 56.34 | savings | | 45678 | 3643.41 | 5280.45 | current | | 56789 | 12878.32 | 10345.00 | current | +---------------+----------+-------------+---------+


Update data in one table with data from another

• The alternative way of updating• 2) Update one table from a value calculated in a

subquery. UPDATE SpyAccount ASET A.income = (SELECT A.income + A.income * R.rate FROM SpyAccRates R WHERE A.atype = R.accType );

• ‘For each row in the SpyAccount table, update income by adding in the income multiplied with the value in the rates table which has a matching account type’

• This only works if the subquery comes up with a matching value. Otherwise it gets more complicated.• ‘only do the above if a match exists’. Not covered now.


Creating Views

• You can create a View which gives you a subset of the data from one or more tablesCREATE VIEW SpyIncrease as

SELECT accountNumber, income, rate,

income*rate as interest

FROM SpyAccount, SpyAccRates

WHERE atype = accType;

+---------------+---------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+---------------+---------------+------+-----+---------+-------+| accountNumber | varchar(5) | NO | | | | | income | decimal(9,2) | NO | | | | | rate | decimal(6,3) | YES | | NULL | | | interest | decimal(15,5) | YES | | NULL | | +---------------+---------------+------+-----+---------+-------+


Creating Views

• You might create a view to• Let someone use the view in their own queries

whilst hiding data they do not have permission to see (e.g. date of birth)

• Simplify complex queries

select * from SpyIncrease+---------------+----------+-------+-----------+| accountNumber | income | rate | interest |+---------------+----------+-------+-----------+| 12345 | 10.20 | 0.020 | 0.20400 | | 13579 | 23930.66 | 0.015 | 358.95990 | | 23456 | 2050.20 | 0.020 | 41.00400 | | 34567 | 362.10 | 0.020 | 7.24200 | | 45678 | 3643.41 | 0.015 | 54.65115 | | 56789 | 12878.32 | 0.015 | 193.17480 | +---------------+----------+-------+-----------+


Using Views

• You can use a view just like a table in a querySELECT accountNumber, income, interest

FROM SpyIncrease

• Every time, the relevant columns and rows will be extracted from the underlying base tables+---------------+----------+----------+

| accountNumber | income | interest |+---------------+----------+----------+| 12345 | 10.20 0.20400 | | 13579 | 23930.66 |358.95990 | | 23456 | 2050.20 | 41.00400 | | 34567 | 362.10 | 07.24200 | | 45678 | 3643.41 | 54.65115 | | 56789 | 12878.32 |193.17480 | +---------------+----------+----------+


Updating using the View

• This is now quite simple! The underlying rows in the SpyAccount table are updated.UPDATE SpyIncreaseSET income = income + interest;

+---------------+----------+-------+-----------+| accountNumber | income | rate | interest |+---------------+----------+-------+-----------+| 12345 | 10.40 | 0.020 | 0.20800 | | 13579 | 24289.62 | 0.015 | 364.34430 | | 23456 | 2091.20 | 0.020 | 41.82400 | | 34567 | 369.34 | 0.020 | 7.38680 | | 45678 | 3698.06 | 0.015 | 55.47090 | | 56789 | 13071.49 | 0.015 | 196.07235 | +---------------+----------+-------+-----------+


SQL Tutorial

• There is a good tutorial on the w3schools site• http://www.w3schools.com/sql/

• Complete reference on the MySQL website

Date post:	16-Dec-2015
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