Transcript A primary key

Database Basics
CPSC 4670/5670
Purpose of a Database
• The purpose of a database is to keep
track of things
• Unlike a list or spreadsheet, a database
may store information that is more
complicated than a simple list
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Database Systems
• The four components of a database system are:
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Users
Database Application
Database Management System (DBMS)
Database
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Users, Database
• A user of a database
system will
• Use a database
application to track
things
• Use forms to enter,
read, delete and
query data
• Produce reports
• A database is a self-describing
collection of related records
• Self-describing
• The database itself
contains the definition of its
structure
• Metadata is data describing
the structure of the
database data
• Tables within a relational
database are related to each
other
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Database Management System (DBMS)
• A database
management system
(DBMS) serves as an
intermediary
between database
applications and the
database
• The DBMS manages
and controls
database activities
• The DBMS creates,
processes and
administers the
databases it controls
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Create databases
Create tables
Create supporting structures
Read database data
Modify database data (insert,
update, delete)
Maintain database structures
Enforce rules i.e., Referential
Integrity Constraints
Control concurrency
Provide security
Perform backup and recovery
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Database Applications
• A database application is a set of one or more
computer programs that serves as an
intermediary between the user and the DBMS
• A database application
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Create and process forms
Process user queries
Create and process reports
Execute application logic
Control database applications
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Desktop Database Systems
• Desktop database systems typically:
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Have one application
Have only a few tables
Are simple in design
Involve only one computer
Support one user at a time
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Organizational Database Systems
• Organizational database
systems typically:
• Support several users
simultaneously
• Include more than one
application
• Involve multiple
computers
• Are complex in design
• Have many tables
• Have many databases
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Commercial DBMS Products
• Example Desktop DBMS Products
• Microsoft Access
• Example Organizational DBMS Products
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Oracle’s Oracle
Microsoft’s SQL Server
IBM’s DB2
InterSystems Caché®
http://www.intersystems.com/cache/
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The Relational Model
Relational Databases
• Relational databases are designed to address
many of the information complexity issues
• A relational database stores information in tables.
Each informational topic is stored in its own
table.
• In essence, a relational database will break-up a
list into several parts. One part for each theme
in the list.
• A Project List would be divided into a CUSTOMER
Table, a PROJECT Table, and a
PROJECT_MANAGER Table
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Entity
• An entity is something of importance to
a user that needs to be represented in
a database
• An entity represents one theme or topic
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Relation
• A relation is a two-dimensional table
that has specific characteristics
• The table dimensions, like a matrix,
consist of rows and columns
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Characteristics of a Relation
• Rows contain data about an entity
• Columns contain data about attributes of the
entity
• Cells of the table hold a single value
• All entries in a column are of the same kind
• Each column has a unique name
• The order of the columns is unimportant
• The order of the rows is unimportant
• No two rows may be identical
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A Sample Relation
EmployeeNumber
100
101
104
107
FirstName
Mary
Jerry
Alea
Murugan
LastName
Abermany
Caldera
Copley
Jacksoni
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A Nonrelation Example
Cells of the table hold multiple values
EmployeeNumber
100
101
104
107
Phone
335-6421,
454-9744
215-7789
610-9850
299-9090
LastName
Abermany
Caldera
Copley
Jacksoni
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A Nonrelation Example
No two rows may be identical
EmployeeNumber
100
101
104
100
107
Phone
335-6421
215-7789
610-9850
335-6421
299-9090
LastName
Abermany
Caldera
Copley
Abermany
Jacksoni
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Terminology
Synonyms…
Table
Row
Column
File or Data file Record
Field
Relation
Attribute
Tuple
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A Key and Uniqueness of Keys
• A key is one (or more) columns of a relation
that is (are) used to identify a row
Unique Key
• Data value is unique
for each row.
• Consequently, the
key will uniquely
identify a row.
Non-unique Key
• Data value may be
shared among several
rows.
• Consequently, the
key will identify a set
of rows.
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A Composite Key
• A composite key is a key that contains two or
more attributes
• For a key to be unique, often it must become a
composite key
• For example,
• To identify a family member, you need to know a
FamilyID, a FirstName, and a Suffix (e.g., Jr.)
• The composite key is:
(FamilyID, FirstName, Suffix)
• One needs to know the value of all three columns to
uniquely identify an individual
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A Candidate and Primary Key
• A candidate key is called “candidate” because it is
a candidate to become the primary key
• A candidate key is a unique key
• A primary key is a candidate key chosen to be the
main key for the relation
• If you know the value of the primary key, you will
be able to uniquely identify a single row
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Relationships Between Tables
• A table may be related to other tables
• For example
• An Employee works in a Department
• A Manager controls a Project
• To preserve relationships, you may need to
create a foreign key
• A foreign key is a primary key from one table
placed into another table
• The key is called a foreign key in the table that
received the key
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Foreign Key Example
Project
Manager
ProjID
MgrID
ProjName
MgrName
Primary Key
MgrID
Foreign Key
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Foreign Key Example
Department
DeptID
DeptName
Location
Employee
Primary Key
EmpID
DeptID
Foreign Key
EmpName
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Referential Integrity
• Referential integrity states that every
value of a foreign key must match a
value of an existing primary key
• For example (see previous slide)
• If EmpID = 4 in EMPLOYEE has a DeptID
= 7 (a foreign key), a Department with
DeptID = 7 must exist in DEPARTMENT
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Referential Integrity
• Another perspective…
The value of the Foreign Key EmployeeID
in EQUIPMENT
must exist in
The values of the Primary Key EmployeeID
in EMPLOYEE
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A Surrogate Key
• A Surrogate Key is a unique, numeric
value that is added to a relation to
serve as the Primary Key
• Surrogate Key values have no meaning
to users and are usually hidden in
forms, queries and reports
• A Surrogate Key is often used in place
of a composite primary key
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Surrogate Key Example
• If the Family Member Primary Key is FamilyID, FirstName,
Suffix, it would be easier to append and use a surrogate
key of FamMemberID
• FamilyID, FirstName and Suffix remain in the relation
• Referential Integrity:
Use…
(FamMemberID) in School must exist in
(FamMemberID) in FamilyMember
Instead of:
(FamilyID, FirstName, Suffix) in School must exist in
(FamilyID, FirstName, Suffix) in FamilyMember
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Functional Dependency
• A relationship between attributes in
which one attribute (or group of
attributes) determines the value of
another attribute in the same table
• Illustration…
• The price of one cookie can determine the
price of a box of 12 cookies
(CookiePrice, Qty)
BoxPrice
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Determinants
• The attribute (or attributes) that we use
as the starting point (the variable on
the left side of the equation) is called a
determinant
(CookiePrice, Qty)
BoxPrice
Determinant
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Candidate/Primary Keys and
Functional Dependency
• By definition…
A candidate key of a relation will functionally
determine all other attributes in the row
• Likewise, by definition…
A primary key of a relation will functionally
determine all other attributes in the row
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Primary Key and Functional
Dependency Example
(EmployeeID)
(ProjectID)
(EmpLastName,
EmpPhone)
(ProjectName,
StartDate)
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Normalization
• Normalization is a process of analyzing
a relation to ensure that it is wellformed
• More specifically, if a relation is
normalized (well-formed), rows can be
inserted, deleted, or modified without
creating update anomalies
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Normalization Principles
• Relational design principles for
normalized relations:
• To be a well-formed relation, every
determinant must be a candidate key
• Any relation that is not well formed should
be broken into two or more well-formed
relations.
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Normalization Example
(StudentID)
(StudentName,
DormName, DormCost)
However, if…
(DormName)
(DormCost)
Then DormCost should be placed into its own relation,
resulting in the relations:
(StudentID)
(StudentName,
DormName)
(DormName)
(DormCost)
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Normalization Example
(AttorneyID,
ClientID)
(ClientName,
MeetingDate, Duration)
However, if…
(ClientID)
(ClientName)
Then ClientName should be placed into its own relation,
resulting in the relations:
(AttorneyID,
ClientID)
(ClientID)
(MeetingDate, Duration)
(ClientName)
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Structured Query Language
(SQL)
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Structured Query Language
• Structured Query Language
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Acronym: SQL
Pronounced as “S-Q-L”
Also pronounced as “Sequel”
Originally developed by IBM as the SEQUEL
language in the 1970s
• SQL-92 is an ANSI national standard
adopted in 1992
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SQL Defined
• SQL is an international standard for
creating, processing and querying
database and their tables.
• SQL is comprised of:
• A data definition language (DDL)
• Used to define database structures
• A data manipulation language (DML)
• Data definition and updating
• Data retrieval (Queries)
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SQL for Data Definition
• The SQL data definition statements
include
• CREATE
• To create database objects
• ALTER
• To modify the structure and/or characteristics
of database objects
• DROP
• To delete database objects
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SQL for Data Definition: CREATE
• Creating database tables
• The SQL CREATE TABLE statement
CREATE
TABLE Employee(
EmpID
Integer
EmpName
Char(25)
);
Primary Key,
Not Null
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SQL for Data Definition: CREATE
with CONSTRAINT
• Creating database tables with PRIMARY
KEY constraints
• The SQL CREATE TABLE statement
• The SQL CONSTRAINT keyword
CREATE
TABLE Employee(
EmpID
Integer
Not Null,
EmpName
Char(25)
Not Null
CONSTRAINT EmpPK
PRIMARY KEY (EmpID)
);
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SQL for Data Definition: CREATE
with CONSTRAINT
• Creating database tables with composite primary
keys using PRIMARY KEY constraints
• The SQL CREATE TABLE statement
• The SQL CONSTRAINT keyword
CREATE
TABLE
EmpID
SkillID
SkillLevel
CONSTRAINT
);
Emp_Skill (
Integer
Integer
Integer,
EmpSkillPK
Not Null,
Not Null,
PRIMARY KEY (EmpID, SkillID)
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SQL for Data Definition: CREATE
with CONSTRAINT
• Creating database tables using PRIMARY KEY and
FOREIGN KEY constraints
• The SQL CREATE TABLE statement
• The SQL CONSTRAINT keyword
CREATE
TABLE
EmpID
SkillID
SkillLevel
CONSTRAINT
CONSTRAINT
CONSTRAINT
);
Emp_Skill (
Integer
Integer
Integer,
EmpSkillPK
EmpFK
EmpID
SkillFK
SkillID
Not Null,
Not Null,
PRIMARY KEY (EmpID, SkillID),
FOREIGN KEY
REFERENCES Employee (EmpID),
FOREIGN KEY
REFERENCES Skill (SkillID)
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SQL for Data Definition: CREATE with CONSTRAINT
• Creating database tables using PRIMARY KEY and FOREIGN
KEY constraints
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The SQL CREATE TABLE statement
The SQL CONSTRAINT keyword
ON UPDATE CASCADE and ON DELETE CASCADE
CREATE
TABLE
EmpID
SkillID
SkillLevel
CONSTRAINT
CONSTRAINT
CONSTRAINT
);
Emp_Skill (
Integer
Not Null,
Integer
Not Null,
Integer,
EmpSkillPK
PRIMARY KEY (EmpID, SkillID),
EmpFK
FOREIGN KEY (EmpID)
REFERENCES
Employee (EmpID)
ON DELETE CASCADE,
SkillFK
FOREIGN KEY (SkillID)
REFERENCES
Skill (SkillID)
ON UPDATE CASCADE
When the row of EmpID (primary key) in Employee TABLE is deleted, the
EmpFK (foreign key) is deleted also.
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Deleting Database Objects: DROP
• To remove unwanted database objects from
the database, use the SQL DROP statement
• Warning… The DROP statement will
permanently remove the object and all data
DROP
TABLE
Employee;
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Removing a Constraint: ALTER
& DROP
• To change the constraints on existing
tables, you may need to remove the
existing constraints before adding new
constraints
ALTER TABLE Employee DROP CONSTRAINT EmpFK;
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SQL for Data Retrieval (Queries)
• SELECT is the best known SQL
statement
• SELECT will retrieve information from
the database that matches the specified
criteria
SELECT
FROM
EmpName
Emp;
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The Results of a Query is a Relation
• A query pulls information from one or
more relations and creates
(temporarily) a new relation
• This allows for a query to:
• Create a new relation
• Feed information to another query (as a
“sub-query”)
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Displaying All Columns: *
• To show all of the column values for the rows
that match the specified criteria, use an *
SELECT
FROM
*
Emp;
Showing a Row Only Once: DISTINCT
• A qualifier may be added to the SELECT
statement to inhibit duplicate rows from
displaying
SELECT DISTINCT
FROM
DeptID
Emp;
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Specifying Search Criteria:
WHERE
• The WHERE clause stipulates the matching
criteria for the record that are to be displayed
SELECT
FROM
WHERE
EmpName
Emp
DeptID = 15;
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Match Criteria
• The WHERE clause match criteria may
include
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Equals “=“
Not Equals “<>”
Greater than “>”
Less than “<“
Greater than or Equal to “>=“
Less than or Equal to “<=“
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Match Operators
• Multiple matching criteria may be
specified using
• AND
• Representing an intersection of the data sets
• OR
• Representing a union of the data sets
SELECT
FROM
WHERE
OR
EmpName
Emp
DeptID < 7
DeptID > 12;
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A List of Values
• The WHERE clause may specify that a particular
column value must be included in a list of values
SELECT
FROM
WHERE
EmpName
Emp
DeptID IN (4, 8, 9);
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The Logical NOT Operator
• Any criteria statement may be preceded by a
NOT operator which is to say that all
information will be shown except that
information matching the specified criteria
SELECT
FROM
WHERE
EmpName
Emp
DeptID NOT IN (4, 8, 9);
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Finding Data Matching a Range of
Values: BETWEEN
• SQL provides a BETWEEN statement that
allows a user to specify a minimum and
maximum value on one line
SELECT
FROM
WHERE
EmpName
Emp
SalaryCode BETWEEN 10 AND 45;
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Allowing for Wildcard
Searches: LIKE
• Sometimes it may be advantageous to
find rows matching a string value using
wildcards
• Single character wildcard character is an
underscore (_)
• Multiple character wildcard character is a
percent sign (%)
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Wildcard Search Examples
SELECT
FROM
WHERE
EmpID
Emp
EmpName LIKE ‘Kr%’;
SELECT
FROM
WHERE
EmpID
Emp
Phone LIKE ‘616-___-____’;
3 underscores
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Sorting the Results: ORDER BY
• The results may be sorted using the
ORDER BY clause
SELECT
*
FROM
Emp
ORDER BY EmpName;
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Built-in SQL Functions
• SQL provides several built-in functions
• COUNT
• Counts the number of rows that match the
specified criteria
• MIN
• Finds the minimum value for a specific column
for those rows matching the criteria
• MAX
• Finds the maximum value for a specific column
for those rows matching the criteria
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Built-in SQL Functions
(continued)
• SUM
• Calculates the sum for a specific column
for those rows matching the criteria
• AVG
• Calculates the numerical average of a
specific column for those rows matching
the criteria
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Built-in Function Examples
SELECT
FROM
COUNT(DISTINCT DeptID)
Emp;
SELECT
MIN(Hours), MAX(Hours),
AVG(Hours)
Project
ProjID > 7;
FROM
WHERE
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Providing Subtotals:
GROUP BY
• Subtotals may be calculated by using
the GROUP BY clause
SELECT
FROM
GROUP BY
HAVING
DeptID, COUNT(*)
Emp
DeptID
Count(*) > 3;
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Retrieving Information from
Multiple Tables
• SubQueries
• As stated earlier, the result of a query is a
relation. As a result, a query may feed another
query. This is called a subquery
• Joins
• Another way of combining data is by using a Join
• Join [also called an Inner Join]
• Left Outer Join
• Right Outer Join
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Subquery
SELECT
EmpName
FROM
Emp
WHERE
DeptID in
(SELECT
DeptID
FROM
Department
WHERE
DeptName
LIKE ‘Accounts%’);
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Join
SELECT EmpName
FROM
Emp, Department
WHERE Emp.DeptID = Department.DeptID
AND Department.DeptName
LIKE ‘Account%’;
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Modifying Data using SQL
• Insert
• Will add a new row in a table
• Update
• Will update the data in a table that
matches the specified criteria
• Delete
• Will delete the data in a table that matches
the specified criteria
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Adding Data: INSERT
• To add a row to an existing table, use
the INSERT statement
INSERT INTO Emp
VALUES (91, ‘Smither’, 12);
INSERT INTO Emp (EmpID, SalaryCode)
VALUES (62, 11);
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Changing Data Values:
UPDATE
• To change the data values in an existing row
(or set of rows) use the Update statement
UPDATE Emp
SET
Phone =‘791-555-1234’
WHERE EmpID = 29;
UPDATE Emp
SET
DeptID = 44
WHERE EmpName LIKE ‘Kr%’;
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Deleting Data: DELETE
• To delete a row or set of rows from a
table using the DELETE statement
DELETE FROM
WHERE
Emp
EmpID = 29;
DELETE FROM
WHERE EmpName
Emp
LIKE ‘Kr%’;
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Movie(title, length)
SELECT title AS name, length * 0.016667 AS lengthInHours
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MovieExec(name, address, cert#, netWorth)
Movies(title, year, length, genre, studioName, producerC#)
StarsIn(movieTitle, movieYear, starName)
SELECT name
FROM MovieExec, Movies, StarIn
WHERE cert# = producerC# AND
title = movieTitle AND
year = movieYear AND
starName = ‘Harrison Ford’
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Movies(title, year, length, genre, studioName, producerC#)
MovieExec(name, address, cert#, netWorth)
StarsIn(movieTitle, movieYear, starName)
SELECT name
FROM MovieExec
WHERE cert# IN
(SELECT producerC#
FROM Movies
WHERE (title, year) IN
(SELECT movieTitle, MovieYear)
FROM StartsIn
WHERE starName = ‘Harrison Ford’)
);
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