Download Introduction to SQL

Section 1 - Introduction to SQL
 SQL is
an abbreviation for Structured
Query Language.
 It is generally pronounced “Sequel”
 SQL is a unified language for... defining,
querying, modifying, and controlling the
data in a Relational Database.
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SQL Standards
 SQL standards
were originally developed in
academia by Dr. E.F. Codd
 Commercial institutions now lead the
standard by extending SQL to meet the
needs of business.
 The main commercial database
management systems (DBMS) in the
industry today are: Oracle, Sybase,
Informix, Microsoft SQL Server
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Interactive SQL
 The
class exercises in use interactive SQL
(i.e. SQL in entered on a command line and
the results are seen automatically in the data
window)
 Embedded SQL, which is SQL that is run
inside of a computer program, is not
covered in the book, but will be a special
topic covered in the class
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SQL as a Second Language
 SQL is
not a “Natural” Language
 SQL is Non Procedural
 SQL has a Definite Syntax
 SQL is freeform, but individual clauses
must be in the proper order
 SQL can not do everything in a single
statement
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Relational Database
 What
is a Relational Database Management
System (RDBMS)?
–
–
–
All data is stored in Tables (i.e. Relations)
(grid-like format, similar to a spreadsheet)
The logical representation of data is separate
from its physical storage
One high-level language is provided for
structuring, querying, and changing
information. This, of course, is SQL
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What is RDBMS? - cont.
 Supports
–
–
–
Selection, Projection and Joins
Selection: What kind of information you see
Projection: The query criteria
Joins: How you connect related information
from different tables
 Supports
the concept of NULL values
 Allows VIEWS into the data
 Provides Mechanisms for Integrity,
Recovery, Authorization, and Transactions
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What are Tables?
 They
have Rows and Columns
(like Files or Spreadsheets)
–
–
Rows (like Records)
Columns (like Fields)
 A Set
of Related Tables is called a Database
 Tables are separate, but equal in that...
–
–
They have no Hierarchical Ranking
They have no necessary Physical Relationship
to each other
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What is an Entity?
 An
entity is a person, place, or thing for
which you wish to hold information
 A table is a collection of separate
occurrences of an Entity
–
E.g. the “Employees” table contains
information about individual employees
 Separate
Characteristics are stored for each
Occurrence of an Entity
–
E.g. An individual employee has a name,
address, phone number, etc.
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Rows & Columns
 A Row
is a single occurrence of an Entity
 Each Column describes one Characteristic
of the Entity
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Example Table
 Last
Name
City
Perry
San Diego
Smith
Los Angeles
Jones
Los Angeles
 In the above table "Last Name" and "City"
are the columns
 Each different person and their represent a
row of data
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Question
 What
is a table?
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Answer
 A table
is a collection of separate
occurrences of an Entity
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Question
 What
is a row?
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Answer
 A Row
is a single occurrence of an Entity
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Question
 Characteristics
of an entity are
described with ___________?
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Answer
 Characteristics
of an entity are
described with COLUMNS ?
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Primary Key
 Each
Row is uniquely identified using the
Primary Key.
 The Primary Key is defined as any Column
(or combination of columns) that can be
used to uniquely identify a particular row.
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Example
 Last
Name
City
Perry
San Diego
Smith
Los Angeles
Jones
Los Angeles
 In the above example the Last Name
column acts as the PRIMARY key. (Note:
names are not usually a good choice, but
this is a simple example)
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Question
 What
is used to distinguish between rows in
a table?
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Answer
 Rows
are distinguished from either other by
using a PRIMARY KEY
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Values
 A Value
can be determined by the
intersection of the Row and Column for the
row identified by the Primary Key.
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Types of Tables
 User
Tables hold the data of the system
 System Tables hold information about the
structure and objects of the database
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Question
 What
is needed to find a specific value in a
table?
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Answer
 The
Primary Key and a Column
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Physical vs. Logical
 The
User’s View of the data is independent
of the physical storage of the data
 Physical storage can change without
affecting the logical representation of the
data.
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SQL is a High-Level Language
 SQL statements
can logically be broken in
to three high-level sets...
 Data Manipulation
DML|
which can query and update the data
 Data Definition
DDL
which defines the objects in a database
 Data AdministrationDCL
which controls access to the data
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Data Manipulation Statements
 The
SELECT statement displays
information you want to see from the
database
 The INSERT statement allow you to add
rows to the database
 The UPDATE statement allows you to
change existing column information
 The DELETE statement deletes rows of
data
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Data Definition Statements
 The
CREATE statement allows you create
tables, views, and indexes
 The DROP statement allows you to remove
tables, views, and indexes
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Data Administration Statements
 The
GRANT statement allows you to define
what userids have access to tables/columns
 The REVOKE statement allows you to
remove userid access to tables/columns
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Select Statement Introduction
 The
next series of pages will show you
some sample tables and data that we will
use to illustrate the Select statement
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Example Tables
 Employees Table
–
–
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Last_name
First_name
City
 ZipCodes Table
–
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City
Zip_code
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Data in Example Tables
 Employees
Last_name
Perry
Smith
Jones
 ZipCodes
First_name
Steve
Will
Tommy Lee
City
San Diego
Los Angeles
Los Angeles
-
City
Zip_code
San Diego
92001
Los Angeles 90211
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Selection
 SELECT last_name,
city
FROM employees
 Results:
Last Name
Perry
Smith
Jones
City
San Diego
Los Angeles
Los Angeles
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Projection
 SELECT last_name,
city
FROM employees
WHERE city = 'San Diego'
 Results:
Last Name
Perry
City
San Diego
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Joins
 SELECT last_name,
city, zip_code
FROM employees, zipcodes
WHERE city = 'San Diego'
AND employees.city = zipcodes.city
 Results:
Last Name
Perry
City
San Diego
Zip Code
92001
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Introducing NULL Values
 NULL means
Unknown, Missing, or Not
Applicable
 NULL does NOT mean Zero or Blank
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Question
 What
kind of SQL statement is used to
Query information in a database?
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Answer
 The
SELECT statements querys
information from the database
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SQL VIEWs
 Views
are 'Derived Tables' that allow a
different view of the data stored in existing
tables
 They are not actual copies of the data
 User may SELECT against them in the
same way as a table
 Also known as 'Virtual tables'
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Integrity, Security, Transactions
 Integrity
insures the consistency and
accuracy of the data
 Security insures proper authorization to
view and/or update the data
 Transactions allow data to be saved to the
database as a logical unit of work
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Question
 TRUE
or FALSE?
A NULL value means an empty string for
character based data
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Answer
 FALSE
a NULL value in numeric, date, or character
based data means Unknown, Missing, or
Not Applicable
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Section 1 - Last Page
 Study
Chapters 2-3 (thru Create statements
only) for Section 2
 There is no Test for Section 1
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