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Informatik II

D-MAVT

Database Queries withSQL

Topic

Database queries with SQL

Program

What is SQL?Creating, altering, and deleting tablesInserting, updating, and deleting data entriesQuerying the databaseQueries across multiple tablesStoring queries as data views

Learning goals

Be able to understand SQL statements andtranslate them to clear text.

Be able to write SQL statements to create/definetables in a database.

Be able to write SQL statements to insert, modify,and delete data in a table.

Be able to write SQL statements to query thedatabase across several tables and with searchconditions.

Database Design Steps

Requirements Analysis (What needs to bestored, for whom, and why?)

Conceptual Modeling (Data entities)

Logical Modeling (Data relationships)

Schema Refinement (Normalization) Physical Model (Mapping to tables)

Implementation (in a RDBMS)

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Further reading

Chapter 3, Simple Queries from SQL for Web Nerds,

Philip Greenspun (http://philip.

greenspun.com/sql/

)

Database Design for Mere Mortals,

Michael J. Hernandez

Information Modeling and Relational Databases,

Terry Halpin

Database Modeling and Design,Toby J. Teorey

What is SQL?

Non-procedural universal language for querying andmanipulating data in RDBMS

Structured Query Language

Many standards out there:

ANSI SQL SQL92 (a.k.a. SQL2) SQL99 (a.k.a. SQL3) Vendors support various sub- or super-sets of these What we discuss is common to all of them

The two parts of SQL

Data Definition Language (DDL) Create/alter/delete tables and their attributes

Data Manipulation Language (DML) Insert/delete/modify entities in tables

Query one or more tables

Data in SQL

1. Atomic data types

2. Table attributes are assigned a data type

SQL is case-insensitive for all commandsand specifiers!

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Basic SQL Commands

Creating tables with CREATE

Adding data with INSERT

Viewing data with SELECT

Removing data with DELETE

Modifying data with UPDATE

Changing tables with ALTER

Destroying tables with DROP

Data Definition Language

SQL commands to define and manipulaterelations in a database.

create tables

alter tables

drop tables

create views (see later)

Creating tables with CREATE

Generic form

CREATE TABLE tablename (

column_name data_type attributes,

column_name data_type attributes,

);

Table and column names cannot have spaces or bereserved words like TABLE, CREATE, etc.

Data Types in SQL

Characters: CHAR(20) -- fixed length

VARCHAR(40) -- variable length

Numbers: BIGINT, INT, SMALLINT, TINYINT

REAL, FLOAT -- differ in precision

MONEY

Times and dates: DATE, TIME

TIMESTAMP

Binary objects (such as pictures, sound, etc.) BLOB -- stands for Binary Large OBject

Others... All are simple

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Column attributes in SQL

Keys: PRIMARY KEY -- primary key of the table

KEY -- foreign key (will be indexed) INDEX -- field to be indexed for fast search

Null values: NOT NULL -- field must be filled in

Default value: DEFAULT value -- value to be used if user gives none

Automatic values: AUTO_INCREMENT -- see later

Others... Most of them are RDBMS-specific

Contact Table: Physical Model

Name Character

Address Character

Company Character

Phone Number Character

URL/Web Page Character

Age Integer

Height Real (float)

Birthday Date

When we added the entry Timestamp

Contact Table: SQL

CREATE TABLE contacts (

Name VARCHAR(40),

Address VARCHAR(60),

Company VARCHAR(60),

Phone VARCHAR(11),

URL VARCHAR(80),

Age INT,

Height FLOAT,Birthday DATE,

WhenEntered TIMESTAMP

);

Plan your tables very carefully!

Once created, they may be difficult to change!

Contact Table: SQL

CREATE TABLE contacts (ContactID INT PRIMARY KEY,Name VARCHAR(40),Address VARCHAR(60),Company VARCHAR(60),Phone VARCHAR(11),URL VARCHAR(80),Age INT,Height FLOAT,

Birthday DATE,WhenEntered TIMESTAMP

);

If you are going to use the relational nature of a database,dont forget you need to have a unique way to access records!

There is a way to make the keyautomatically increment,so you dont have to worry about which one is next.

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Automatic key generation

AUTO_INCREMENT field attribute:

CREATE TABLE contacts (ContactID INT PRIMARY KEYAUTO_INCREMENT,Name VARCHAR(40),

Database automatically gives sequentialnumbers to the entities

Makes sure each number is unique

Numbers will never change once assigned

Number value has no real-world meaning

Another Create Table Example

CREATE TABLE customer(cust_id INT,name VARCHAR(50) NOT NULL,address VARCHAR(256) NOT NULL,

PRIMARY KEY (cust_id));

CREATE TABLE credit_card(cust_id INT NOT NULL,credit_card_type CHAR(5) NOT NULL,credit_card_num INT NOT NULL,

KEY (cust_id));

Customer

have

N

1

nameaddress

Credit card

card numbercard type

Modifying Tables

Examples:

ALTER TABLEcustomerMODIFY COLUMN nameVARCHAR(256);

ALTER TABLE customerADD COLUMNcredit_limit REAL;

Generic form

ALTER TABLE tablename

alter specifications, ;

ALTER specifications

| ADD [COLUMN] column_definition [FIRST | AFTER col_name ]| ADD {INDEX|KEY} [index_type] (index_col_name,...)| MODIFY [COLUMN] column_definition [FIRST | AFTER col_name]| DROP [COLUMN] col_name| DROP PRIMARY KEY| DROP {INDEX|KEY} index_name

| DROP FOREIGN KEY fk_symbol| RENAME [TO] new_tbl_name

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Destroying tables with DROP

Generic Form

DROP TABLE tablename;

Example:

DROP TABLE contacts;

ATTN: All data will be destroyed along with the table.

The system will not ask twice!

Data Manipulation Language

SQL commands to manipulate the data in adatabase or query the database.

insert new data entries

update existing entries

delete entries

query the database

Adding data with INSERT

Generic Form

INSERT INTO tablename (column_name,)

VALUES (value,)

Inserting a record into contacts

INSERT INTO contacts(contactid,name,address,company,phone,url,age,height,birthday,whenentered)

VALUES

(1,Joe,123 Any St.,ABC,

800-555-1212,http://abc.com,30,1.9,6/14/1972,now());

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Inserting a partial record

INSERT INTO contacts(contactid,name,phone)

VALUES (2,Jane,212-555-1212);

Modifying data with UPDATE

Generic Form

UPDATE table SET column=expression

WHERE condition;

Example:

UPDATE contacts SET company=AOL

WHERE company=Time Warner;

Removing data with DELETE

Generic Form

DELETE FROM table WHERE condition;

Example:

DELETE FROM contacts WHERE age

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Lets start simple

Simplified generic form:

Multiple tables can be joined in a single query

Multiple conditions (search criteria) can be imposed

Results can be sorted or grouped

SELECT attributesFROM table(s)WHERE conditions

Simple SQL Query

HitachiHousehold$203.99MultiTouch

CanonPhotography$149.99SingleTouch

GizmoWorksGadgets$29.99PowergizmoGizmoWorksGadgets$19.99Gizmo

SupplierCategoryPricePName

SELECT *

FROM Product

WHERE category=Gadgets

Product

GizmoWorksGadgets$29.99Powergizmo

GizmoWorksGadgets$19.99Gizmo


selection

Simple SQL Query






SELECT PName, Price, Supplier

FROM Product

WHERE Price > 100

Hitachi$203.99MultiTouch

Canon$149.99SingleTouch

SupplierPricePName

selection and

projection

Product

Eliminating Duplicates

Compare to:

SELECT DISTINCT category

FROM ProductHousehold

Photography

Gadgets

Category

SELECT category

FROM ProductHousehold

Photography

Gadgets

Gadgets

Category

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More SELECT examples

SELECT * FROM contacts;

Display all records in the contacts table

SELECT contactid,name FROM contacts;

Display only the record number and names

SELECT DISTINCT url FROM contacts;

Display only one entry for every value of URL.

Selection Operations

What goes in the WHERE clause:

x = y, x < y, x

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The LIKE operator

sLIKEp: pattern matching on strings

p may contain two special symbols: % = any sequence of characters

_ = any single character

Product(Name,Price,Category,Supplier)

Find all products whose name contains gizmo:

SELECT *FROM ProductsWHERE PName LIKE %gizmo%

More LIKE examples

The LIKE condition

Allows you to look at strings that are alike SELECT * FROM contacts

WHERE name LIKE J%;

Display records where the name starts with J

SELECT * FROM contactsWHERE url NOT LIKE %.com;

Display where url does not end in .com

Ordering the Results

SELECT pname, price, supplier

FROM Product

WHERE category=gadgets AND price > 50

ORDER BY price ASC

ASC order in ascending order DESC in descending order List of several attributes can be given for nested

ordering (e.g. order by price first and within all productsof same price, order by supplier:

ORDER BY price, supplierASC)


SELECT category

FROM Product

ORDER BY Pname ASC




GizmoWorksGadgets$19.99GizmoSupplierCategoryPricePName

?Photography

Gadgets

Household

GadgetsCategory

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SELECT DISTINCT category

FROM Product

ORDER BY categoryPhotography

Household

Gadgets

Category

Joins in SQL

Connect two or more tables:





SupplierCategoryPricePNameProduct

Company

Japan15Hitachi

Japan65Canon

USA25GizmoWorks

CountryStockPriceCName

What isthe Connection

betweenthem ?

Joins

Product(pname,price,category,supplier)

Company(cname,stockPrice,country)

Find all products under $200 manufactured in Japan;

return their names and prices.

SELECT PName, Price

FROM Product, Company

WHERE Supplier=CName AND Country=Japan

AND Price

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Joins


Company(cname,stockPrice,country)

Find all countries that manufacture some product in the

Gadgets category.

SELECT Country


WHERE Supplier=CName AND Category=Gadgets

Joins in SQL



GizmoWorksGadgets$29.99PowergizmoGizmoWorksGadgets$19.99Gizmo


Product Company

Japan15Hitachi

Japan65Canon

USA25GizmoWorks

CountryStockPriceCname

USA

USA

Country

Why doesUSA appear

twice ?

SELECT Country



Internal joint table






RDBMS internally builds a joint table with ALL matches:

USA25GizmoWorks

Japan15Hitachi

Japan65Canon

USA25GizmoWorks

CountryStockPriceCname

USA

USA

Country

SELECT Country



First the tables are joint and entries duplicatedThen the selection is made!

Disambiguating Attributes

Sometimes two relations have the same attr:Person(pname,address,worksfor)

Company(cname,address)

SELECT DISTINCT pname, address

FROM Person, CompanyWHERE worksfor=cname

SELECT DISTINCTPerson.pname, Company.address

FROM Person, CompanyWHERE Person.worksfor=Company.cname

Which

address ?

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In fact table names introduced automatically by the system:

Company(cname,address)

Becomes:

It NEEDS to be done by hand if column names areambiguous!

SELECT cname

FROM Company

SELECT Company.cname

FROM Company

Joining together multiple tables

SELECT name,phone,zip FROMpeople, phonenumbers, addressWHEREpeople.addressid=address.addressidANDpeople.id=phonenumbers.id ;

3Chris3

2Jane2

1Joe1

AddressidNameId

People

14423789PDQ3

14454456XYZ2

12345123ABC1

ZipAddressCompanyAddressID

Address

321136

234135

342124

321113

223412

553211

PhoneIdPhoneID

PhoneNumbers

Multiple Joins


Purchase(buyer,seller,store,product)

Person(persname,phoneNumber,city)

Find names of people living in Seattle that bought some

product in the Gadgets category, and the names of the

stores they bought such product from

SELECT DISTINCT persname, store

FROM Person, Purchase, Product

WHERE persname=buyer AND product=pname AND

city=Seattle AND category=Gadgets

Examples

1Max

Alice

2John

TutorIDName

Fabiana3

Greg2

Bob1

NameID

Students

Tutors

BobMax

NULLAlice

GregJohn

Tutor.NameStudent.Name

BobMax

GregJohn


FabianaNULLGregJohn

BobMax


inner

left outer

right outer

BobMax

FabianaNULL

NULLAlice

GregJohn

Tutor.NameStudent.Namefull outer

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Different types of JOINs

Inner Join Unmatched rows in either table arent printed

Left Outer Join All records from the left side are printed. NULLs are filled in ifno match on the right side can be found.

Right Outer Join All records from the right side are printed. NULLs are filled in if

not match on the left side is found.

Full Outer Join All records are printed. NULLs are filled in for missing records on

either side.

Natural Join Attributes of the same name are automatically joined

General form of SELECT/JOIN

SELECT columns,

FROM left_tablejoin_type JOIN right_table ON condition;

SELECT name,phone FROM people

JOIN phonenumbers ONpeople.id=phonenumbers.id;

Join type examples


LEFT JOIN phonenumbers ONpeople.id=phonenumbers.id;


RIGHT JOIN phonenumbers ON

people.id=phonenumbers.id;


FULL JOIN phonenumbers ONpeople.id=phonenumbers.id;

Theta style vs. ANSI

Theta Style (only forequi-joins)

SELECT name,phone,zip FROM people, phonenumbers, address

WHERE people.addressid=address.addressid ANDpeople.id=phonenumbers.id ;

ANSI Style (for all join types)

SELECT name,phone,zip FROM people

JOIN phonenumbers ON people.id=phonenumbers.id

JOIN address ON people.addressid=address.addressid;

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Tuple Variables

SELECT DISTINCT x.buyer, x.seller

FROM Purchase AS x

WHERE x.store = BestBuy

Find buyer and seller of all purchases that were made instore BestBuy:


Saves typing with long table names!

Tuple VariablesTuple variables introduced automatically by the system:

Product(name,price,category,supplier)

Becomes:

They NEED to be specified manually when the same tableappears more than once!

SELECT name

FROM Product

WHERE price > 100

SELECT Product.name

FROM Product AS Product

WHERE Product.price > 100

Tuple Variables

SELECT DISTINCT x.storeFROM Purchase AS x, Purchase AS y

WHERE x.product = y.product AND y.store = BestBuy

Find all stores that sold at least one product that the storeBestBuy also sold:



Person(persname,phoneNumber,city)

JOIN of a table with itself.

Renaming Columns






SELECT Pname ASprodName, Price ASaskPrice

FROM Product

WHERE Price > 100

Product

$203.99MultiTouch

$149.99SingleTouch

askPriceprodName

Query with

renaming

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GROUP BY/HAVING

The GROUP BY clause allows

you to group results together beforeapplying aggregation functions like:

AVG(), COUNT(), MAX(), MIN(), SUM()

COUNT DISTINCT

HAVING allows you to searchthe grouped results

GROUP BY/HAVING

7100Oracle

4500IBM

5500Oracle

AmountCustomer 17100Oracle

17100IBM

17100OracleAmountCustomer

4500IBM

12600Oracle

AmountCustomer

SELECT customer, SUM(amount)FROM Sales;

Sales

SELECT customer, SUM(amount)FROM Sales GROUP BY customer;

GROUP BY/HAVING

7100Oracle4500IBM

5500Oracle

AmountCustomer

12600Oracle

AmountCustomer

SELECT customer, SUM(amount)FROM Sales GROUP BY customerWHERE SUM(amount)>10000;

Sales

SELECT customer, SUM(amount)FROM Sales GROUP BY customerHAVING SUM(amount)>10000;

4500IBM

12600Oracle

AmountCustomer

SUM(amount)=17100which is always >10000!

==> Cannot use WHERE

GROUP BY Examples

SELECT company,count(company)FROM contactsGROUP BY company; How many times does each company appear in

the contacts table?

SELECT company,count(company)FROM contactsGROUP BY companyHAVING count(company) > 5; Only show counts for companies that appear

more than 5 times.

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Nested SELECTs

The WHERE subclause of a SELECTstatement can contain another SELECT

statement:

SELECT * FROM contactsWHERE zip NOT IN (

SELECT zip FROM addressWHERE state=NY

);

(Select all contacts that have a ZIP code outside NY state.)

Nested SELECTs

RDBMS starts with the inner-mostSELECT and executes it

Results are pasted into query in place ofthe executed SELECT

Progress outward recursively until outer-most SELECT has been executed

Views in SQL

An SQL view is a virtual table that is derivedfrom other real or virtual tables

Real tables are defined by CREATE TABLEcommands and are permanently stored in thedatabase

Virtual tables are defined by the CREATE VIEW

command to avoid defining complex SQLretrieval expressions repeatedly

Only the definition of a view is stored, but not thedata inside. They are recomputed every time theview is used (opened)

Creating and Deleting Views

Generic form of View definition

CREATE VIEW viewname AS(SELECT-Statement);

Deleting a view

DROP VIEW viewname;

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Example of a View definition

Views are stored queries and are created onthe basis of a SELECT statement:

CREATE VIEW contactview AS

(SELECT name,phone,zip FROM

people,phonenumbers,address

WHERE people.id=phonenumbers.id ANDpeople.addressid=address.addressid);

Views can be used in other SELECT statementsas if they were tables.

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