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And Franchise Colleges
HSQ - DATABASES & SQL
3 SQL Overview
By MANSHA NAWAZ
Section 3
SQL Overview
1
OVERVIEW
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•
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•
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Library Database – ERD
Library Database - Tables
Structured Query Language (SQL)
SQL Usage
SQL Commands
SQL Data Definition Language (DDL)
SQL Data Manipulation Language (DML)
Section 3
SQL Overview
2
Library Database – ERD
The library
model used to
demonstrate SQL
ERD: Library
Section 3
SQL Overview
3
Library Database - Tables
Publisher (publisher-code, publisher-name)
The library
tables used to
demonstrate SQL
Limit (borrower-status, loan-limit)
Borrower (bor_no, bor-name, bor-state, addr1, addr2, town, postcode)
Copies (access_no, isbn, buy-price, buy_date)
Book (isbn, pub_code, title, pub_date, now_price)
Authorship (isbn, author_name)
Loan (access_no, bor_no, loan-date)
Reservation (bor_no, isbn, reserve-date)
•
The data tables are on the website.
Section 3
SQL Overview
4
Library Database - Tables
The library
tables used to
demonstrate SQL
LIBRARY DATABASE
MS Access 2000
Section 3
MS SQL – Query Analyzer
Meta File
SQL Overview
MS SQL – Enterprise Manager
5
Structured Query Language (SQL)
•
SQL was developed by IBM in the 1970s for use in System R. It is the de facto
standard as well as being an ISO and ANSI standard.
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It is often embedded in general purpose programming languages.
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The first SQL standard, in 1986, provided basic language constructs for
defining and manipulating tables of data; a revision in 1989 added language
extensions for referential integrity and generalised integrity constraints.
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Another revision in 1992 provided facilities for schema manipulation and data
administration, as well as substantial enhancements for data definition and
data manipulation.
•
SQL is the most popular, and now standard, language for manipulating data
in a relational database. Developers and Users can use SQL to interrogate
databases.
Section 3
•
•
•
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Creating,
Accessing
Searching
Modifying
SQL Overview
6
SQL Usage
• SQL used by many different DBMS:
• Oracle
• Microsoft SQL Server
• MS Access
• Sybase etc.
• Database Management System (DBMS) interfaces provided in MS
Access and MS SQL Server are wrote in SQL.
• Initially we will examine SQL under MS Access
– non-standard sql
• In the main we use MS SQL Server 2000
– standard sql
• SQL is the most popular, and now standard, language for
manipulating tables in a relational database is SQL.
Section 3
SQL Overview
7
SQL Commands
• SQL are a combination of commands classified as:
• Data Definition Language (DDL)
– DDL is used to specify the data in a database.
– The DDL statements define database objects, eg databases, tables, views,
indexes, users, constraints, user-defined data types: CREATE, DROP, ALTER
– A full guide is provided here
• Data Manipulation Language (DML)
– DML is used to access the data in a database.
– The DML statements manipulate data: SELECT, INSERT, DELETE, UPDATE
– A full guide is provided here
• Data Control Language (DCL)
– DCL is used to control access to the data in a database.
– The DCL statements control access to data: GRANT, DENY, REVOKE
Section 3
SQL Overview
8
Data Definition Language (DDL)
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SQL provides a Data Definition Language
(DDL) to create and maintain defined
database objects
Databases
Tables
Views
Indexes
Users
Constraints
1. CREATE TABLE
2. CREATE TABLE and Foreign Keys
user-defined data types:
3. CREATE INDEX
•
This is a demonstration guide to using SQL
4. CREATE VIEW
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SQL examples generally based on the
Library Database
5. CREATE TRIGGER
•
6. DROP TABLE
The DDL statements build our Data Model
Section 3
SQL Overview
9
CREATE TABLE
•
•
SQL command to generate a new table.
Syntax:
– create table "tablename“
– ("column1" "data type" [optional constraint], "column2" "data type"
[optional constraint], "column3" "data type" [constraint]);
– Data types: char, int, varchar, etc.
– Constraints: identity, primary key, default
Examples of Create Table
create table students
(
studentID char(9) not null primary key,
firstName varchar(15) not null,
lastName varchar(20) not null,
grade char(2),
)
Section 3
SQL Overview
10
CREATE TABLE and Foreign Keys
The syntax for describing tables takes the following format.
CREATE TABLE publisher (
pub_code
CHAR(4) NOT NULL,
pub_name
CHAR(20) NOT NULL,
CONSTRAINT pub_primary_key PRIMARY KEY (pub_code));
•
The NOT NULL indicates that a value must always be present for that attribute.
– The primary key is defined through a ‘constraint’.
• Notice that the constraint is named.
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If a table is created, but later a new column needs to be added:
ALTER TABLE table_name
ADD column_name data_type;
Section 3
SQL Overview
11
CREATE TABLE and Foreign Keys
•
Defining both primary and foreign keys.
CREATE TABLE BOOK (
isbn
CHAR(8) NOT NULL,
pub_code
CHAR(4),
title
CHAR(40),
pub_date
CHAR(4),
now_price
NUMBER(10,2),
CONSTRAINT bookpublisher FOREIGN KEY (pub_code)
REFERENCES publisher (Pub_code),
CONSTRAINT book_primary_key PRIMARY KEY (isbn));
Section 3
SQL Overview
12
CREATE INDEX
•
Improving database performance.
– Indexes are essentially "look up" tables on a given set of attributes, and can
improve the performance of a database.
•
UNIQUE indexes provide the facility for the implementation of table identifiers this is how a primary key constraint works.
CREATE UNIQUE INDEX pub_index
ON publisher (pub_code);
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To create a secondary (non unique index:
CREATE INDEX res_index
ON reservation (reserve_date);
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DROP INDEX - Remove an index
DROP INDEX res_index;
Section 3
SQL Overview
13
CREATE VIEW - Virtual Tables
•
Views are virtual tables that are derived from other views or from tables that
exist in a database (so called "base" tables).
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So to create a view of just the publisher_names from the Publisher table.
CREATE VIEW publish_name(publishers)
AS
SELECT pub_name
FROM publisher;
Section 3
SQL Overview
14
•
PUBLISHERS
Legend Books
Arrow Books
Penguin Books
Nel Paperback
Hodder & Stoughton
Corgi Books
Granada Publishing
Futura Publications
Sphere Books
Mandarin Paperbacks
Orbit Books
The view would therefore form the
following virtual table.
SELECT * FROM publish_name
•
Another example:
CREATE VIEW books_at_499
AS
SELECT title, now_price
FROM book
WHERE now_price = 4.99;
title
Contact
Xenocide
The Smoke Ring
now_price
4.99
4.99
4.99
SELECT * FROM now_price = 4.99;
Section 3
SQL Overview
15
Views using Multiple tables
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Creating a VIEW with 2 base tables.
CREATE VIEW loan_names(bookloan, member)
AS
SELECT loan.access_no, borrower.bor_name
FROM loan, borrower
WHERE borrower.bor_no = loan.bor_no;
SELECT * FROM loan_names;
Section 3
SQL Overview
bookloan
A100012101
A100012102
A100012103
A100156102
A100156103
A100159102
A100162102
A100262101
A100400102
A100420101
A100430101
A100477744
member
Ozeke K
Smith P
Ozeke K
Spawton P
Dixon G
Smith P
Majathia R
Ozeke K
Fraser K
Dixon G
Singh L
Smith P
16
VIEWS of VIEWS
•
Views can, once created, be used in SELECT statements, as if they actually
exist as a table.
SELECT title
FROM books_at_499;
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Views can also be defined based on other views.
CREATE VIEW smithloan
AS
SELECT *
FROM loan_names
WHERE member = 'Smith*';
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DROP VIEW - Remove an existing view
•
DROP VIEW loan_names;
Section 3
SQL Overview
17
CREATE TRIGGER
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A trigger is a set of SQL code that is automatically executed whenever an
associated action is performed
Example:
•
To have the entire table outputted whenever we insert an entry
Create Trigger dispAllEntries
on students
for insert as
select * from students
Section 3
SQL Overview
18
DROP TABLE
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Remove an existing table
DROP TABLE table_name;
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To eliminate the publisher table, you would use:
DROP TABLE publisher;
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To eliminate the student table, you would use:
DROP TABLE students
Section 3
SQL Overview
19
End of Data Definition Language
Section 3
SQL Overview
20
Data Manipulation Language (DML)
•
SQL is a Data Manipulation Language (DML)
used to develop and manipulate data in a
relational database is SQL.
•
This is a demonstration guide to using SQL
•
SQL examples generally based on the Library
Database
•
The DML statements manipulate data:
1. SELECT
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
SELECT & FROM
WHERE CLAUSE
ORDER BY
DISTINCT
BETWEEN and LIKE
IN and NOT IN
Joining Tables
Aliases for Tables
More on Joins
Examining the Joins
Sub-Queries
13. INSERT
14. CREATE TRIGGER
15. DELETE
16. UPDATE
Section 3
SQL Overview
21
DML OVERVIEW
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DML is used for the manipulation of data in a database via by applications and/or
directly by end-users.
As a relational database is a collection of tables with associated data it can be seen to
be made up of two parts. The first part is the structure of the tables and their columns
and the second part is the data that will be stored in these columns to form the
database.
SQL provides language facilities that enable the definition of the structure of the
tables and their columns and language facilities for the maintenance and
manipulation of the data that will be stored in the tables. In this module we are
concerned with the manipulation and maintenance of the data that is stored in the
database.
The part of the SQL language that covers this area is know as the Data Manipulation
Language or DML for short.
The DML is the subset of the SQL language which invokes actions from the DBMS to
manipulate data in the database. The actions in the database are guaranteed by the
DBMS to maintain the integrity of the data in the database.
The application programs issue DML commands to change the contents of the
database to reflect changes in the real world data. Using DML statements you can:
Select data from a table, which can be specified precisely using clauses in the SQL
statement.
–
–
–
Insert data values into tables as rows.
Update existing data values in rows.
Delete certain rows from certain tables. SQL contains DML commands such as INSERT, UPDATE,
and DELETE
Section 3
SQL Overview
22
SELECT
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Select is used to retrieve desired portions of the database
Optional conditional statement where is used to discriminate among the
entries
Conditions: <, =, <>, LIKE... And also use wildcard operator %
Syntax:
– select "column1" [,"column2",etc]
– from "tablename"
– [where "condition"]
note: [] = optional
Examples of Select
•
Matching any last names that end in ‘s’:
select firstName, lastName
from students
where last LIKE '%s‘
•
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Getting all fields of all entries back:
select * from students
Finding Darryn
select * from students where firstName = ‘Darryn'
Section 3
SQL Overview
23
Other things we can do with Select
• Select is the most powerful command, and it deserves more
attention
• Other things that we can do with select:
–
–
–
–
–
Finding minimum, maximum, average etc. values
Group entries by similar values in specific columns
Performing arithmetic or sorting on entries
Joining tables
Countless others
Section 3
SQL Overview
24
SELECT & FROM
•
A simple example
SELECT bor_state
FROM limit;
BOR_STATE
1
2
3
4
5
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If we want to see all columns in a table then we could write them out explicitly,
as follows:
SELECT access_no, isbn, buy_price, buy_date
FROM copies;
or:
SELECT *
FROM copies;
Section 3
SQL Overview
25
WHERE CLAUSE
SELECT *
FROM book
WHERE now_price > 5;
•
If we only wanted book details for the books with isbn '86007906', then the
query would be:
SELECT *
FROM book
WHERE isbn = '86007906';
•
If we wanted book details for books with NOW_price 4.99 or 5.99,
SELECT *
FROM book
WHERE now_price = 4.99 OR now_price = 5.99;
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AND, OR & NOT can be used in WHERE statements.
Section 3
SQL Overview
26
ORDER BY
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If you wish to be sure of a sequence of output then the ORDER BY clause is
appended to the basic SQL statement.
SELECT *
FROM publisher
ORDER BY pub_name;
Or ..
SELECT *
FROM book
WHERE pub_date > '1989'
ORDER BY pub_date, title;
ISBNX
PUB_CODE
09946950
LEGD
55213703
PUB_DATE
NOW_PRICE
Contact
1990
4.99
CORG
Good Omens
1990
3.99
70884440
FUTR
The Ascension Factor
1990
3.99
09952500
ARRW
Xenocide
1991
4.99
45057717
HODD
Mars
1993
5.99
Section 3
TITLE
SQL Overview
27
DISTINCT
•
Some retrievals may result in table outputs that have
duplicate rows.
– For instance, the following query produces a
table with duplicate rows.
SELECT bor_no
FROM reservation;
•
gives:
To eliminate the duplicates, the DISTINCT
operator is applied to the column in the SELECT
statement, as follows.
SELECT DISTINCT bor_no
FROM reservation;
gives:
Section 3
SQL Overview
BOR_NO
B0000006
B0000004
B0000004
B0000009
B0000007
B0000002
B0000008
B0000007
BOR_NO
B0000006
B0000004
B0000009
B0000007
B0000002
B0000008
28
BETWEEN and LIKE
•
BETWEEN
SELECT *
FROM book
WHERE now_price BETWEEN 4.45 AND 5.49;
•
LIKE
SELECT *
FROM author
WHERE author_name LIKE '%Pr%';
– Note the % character for a wildcard rather than
– Why not
Section 3
*
* use as usual?
SQL Overview
29
IN and NOT IN
•
These are used to find rows where values of the required attribute match any
one of a set of values, or fail to match any of the set of values.
SELECT *
FROM book
WHERE now_price IN [ 4.99, 5.99 ] ;
– This would look for details of books with a current price of 4.99 or 5.99.
•
NOT IN provides the reverse of IN, so;
SELECT *
FROM book
WHERE pub_date NOT IN ['1980','1986'];
– What does this do?
Section 3
SQL Overview
30
Joining Tables
•
The most important aspect of SQL!
•
Sometimes, in order to satisfy a query, data from more than one table needs to
be output or manipulated as part of that query.
SELECT bor_name
FROM borrower, reservation
WHERE borrower.bor_no = reservation.bor_no;
•
This lists the names of the borrowers
for every RESERVATION. (Why are
some repeated?)
Section 3
SQL Overview
bor_name
Spawton P
Majathia R
Majathia R
Smith P
Fraser F
Fraser F
Rizzo H
Smith W
31
Aliases for Tables
•
This allows you to declare a short name for a table inside an SQL statement.
SELECT b.bor_no, b.bor_name, r.isbn
FROM borrower b, reservation r
WHERE b.bor_no = r.bor_no ;
•
This stops SQL code being quite so longwinded.
– Strictly you don't need to use an alias for an attribute that is in only one table within
the query.
– In this case we only need the alias for bor_no.
•
The main purpose of aliases is to allow the use of a table more than once.
Section 3
SQL Overview
32
More on Joins
•
Supposing we had wanted, for all reservations, the bor_no and bor_name
along with the title of each book.
We need to link all three tables
BORROWER
1
by
m
RESERVATION
m
of
1
BOOK
BOOK(isbn, pub-code, title, pub-date, now-price)
BORROWER(bor-no, bor-name, bor-state, addr1, addr2, town, postcode)
RESERVATION(bor_no, isbn, reserve-date)
•
Can you see the attributes to join on?
Section 3
SQL Overview
33
•
The bor_name is in the borrower table and the title is in the book table
•
The reservation table has to be joined with the other two tables.
•
Notice:
bor_no is in both reservation and borrower.
isbn is in both reservation and book.
•
So … can you write the query?
SELECT br.bor_no, br.bor_name, bk.isbn, bk.title
FROM borrower br, reservation r, book bk
WHERE br.bor_no = r.bor_no
AND r.isbn = bk.isbn;
Section 3
SQL Overview
34
Examining the Joins
•
Notice how simple it is to write the syntax for the two joins.
BORROWER
RESERVATION
br.bor_no = r.bor_no
•
BOOK
r.insbx = bk.isbnx
The original tables - can you see how it works?
BOOK(isbn, pub-code, title, pub-date, now-price)
BORROWER(bor-no, bor-name, bor-state, addr1, addr2, town, postcode)
RESERVATION(bor_no, isbn, reserve-date)
Section 3
SQL Overview
35
Sub-Queries
•
Sub-queries can be used as an alternative to joining tables. Sub-queries simply
allow you to write a join in another, often simpler way.
•
A standard join:
SELECT bor_name
FROM borrower, reservation
WHERE borrower.bor_no = reservation.bor_no;
– This finds the name of all borrowers who have made reservations.
•
Written as a sub-query:
SELECT bor_name
FROM borrower
WHERE bor_no IN
(SELECT bor_no
FROM reservation);
Section 3
SQL Overview
36
Sub-Queries cont.
•
Sub-queries can be very useful because they can retrieve data without
introducing aliases.
•
For example: Find all the books published by publishers other then the
publisher who published 'Foundation and Empire':
SELECT isbn, title
FROM book
WHERE pub_code NOT IN
(SELECT pub_code
FROM book
WHERE title = 'Foundation and Empire');
•
We can imagine that the lower half of the query feeds the PUB_CODE of any
matching books up to the top level.
Section 3
SQL Overview
37
INSERT
•
•
Insert an entry into a table
Syntax:
– insert into "tablename“
– (first_column,...last_column) values
– (first_value,...last_value);
Example of Insert
insert into students
(studentID, firstName, lastName)
values('u63773941','Tarik','Borogovac')
Section 3
SQL Overview
38
CREATE TRIGGER
•
A trigger is a set of SQL code that is automatically executed whenever an
associated action is performed
Example:
•
To have the entire table outputted whenever we insert an entry
Create Trigger dispAllEntries
on students
for insert as
select * from students
Section 3
SQL Overview
39
DELETE
• Used to delete a record matching certain criteria
• Syntax:
delete from "tablename“
where "columnname" OPERATOR "value" [and|or "column" OPERATOR "value"];
Example of delete
delete from students
where lastName = ‘Campbell'
Section 3
SQL Overview
40
UPDATE
•
•
Used to change a record.
Syntax:
update "tablename"
set "columnname" = "newvalue" [,"nextcolumn" = "newvalue2"...]
where "columnname" OPERATOR "value" [and|or "column" OPERATOR "value"];
Example of Update
update students
set firstName = 'darryn', lastName='campbell'
where studentID='u63773941'
Section 3
SQL Overview
41
FURTHER READING
• Review the attached set of SQL notes over the next four weeks
to reinforce your SQL skills.
– Data Models are converted to schemas which are readable by the database
management system.
– Notation standardised through SQL and XML
– Schemas describe data.
– Described as tables (relations) for relational databases.
– Definition of Columns of tables based on domains (sets of valid values).
– Metadata describes data. Schemas form part of the metadata for a system.
Key Relational and SQL
Concepts (part 1 of 3)
SQL_Data_Definition
SQL Sub Queries
Section 3
Key Relational and SQL
Concepts (part 2 of 3)
Domains
Metadata
SQL Groups
SQL Overview
Key Relational and SQL
Concepts (part 3 of 3)
XML
SQL Data Definition Views
42
End of Data Manipulation Language
Section 3
SQL Overview
43