Section 3SQL Overview1 HSQ - DATABASES & SQL And Franchise Colleges 3 SQL Overview By MANSHA NAWAZ.

Section 3 SQL Overview 1

HSQ - DATABASES & SQL

And Franchise Colleges

3 SQL Overview

By MANSHA NAWAZ


OVERVIEW

• Library Database – ERD • Library Database - Tables• Structured Query Language (SQL)• SQL Usage• SQL Commands• SQL Data Definition Language (DDL)• SQL Data Manipulation Language (DML)


Library Database – ERD

ERD: Library

The librarymodel used to

demonstrate SQL


Library Database - Tables

Publisher (publisher-code, publisher-name)

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.

The librarytables used to

demonstrate SQL


Library Database - Tables The librarytables used to

demonstrate SQL

LIBRARY DATABASE

MS Access 2000 MS SQL – Query AnalyzerMeta File

MS SQL – Enterprise Manager

Library.mdb Library.Schema


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.

• It is often embedded in general purpose programming languages.

• 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.

• 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.

• Creating, • Accessing• Searching• Modifying


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.


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


1. CREATE TABLE

2. CREATE TABLE and Foreign Keys

3. CREATE INDEX

4. CREATE VIEW

5. CREATE TRIGGER

6. DROP TABLE

Data Definition Language (DDL)

• SQL provides a Data Definition Language (DDL) to create and maintain defined database objects

Databases Tables

Views Indexes

Users Constraints

user-defined data types:

• This is a demonstration guide to using SQL

• SQL examples generally based on the Library Database

• The DDL statements build our Data Model


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),)

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


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.

• If a table is created, but later a new column needs to be added:

ALTER TABLE table_name

ADD column_name data_type;

CREATE TABLE and Foreign Keys


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));


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);

• To create a secondary (non unique index:CREATE INDEX res_index

ON reservation (reserve_date);

• DROP INDEX - Remove an indexDROP INDEX res_index;


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).

• 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;


• The view would therefore form the following virtual table.

SELECT * FROM publish_name

PUBLISHERSLegend BooksArrow Books

Penguin BooksNel Paperback

Hodder & StoughtonCorgi Books

Granada PublishingFutura Publications

Sphere BooksMandarin Paperbacks

Orbit Books

• Another example:CREATE VIEW books_at_499

AS

SELECT title, now_price

FROM book

WHERE now_price = 4.99;

SELECT * FROM now_price = 4.99;

title now_priceContact 4.99Xenocide 4.99The Smoke Ring 4.99


Views using Multiple tables

• 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;

bookloan memberA100012101 Ozeke KA100012102 Smith PA100012103 Ozeke KA100156102 Spawton PA100156103 Dixon GA100159102 Smith PA100162102 Majathia RA100262101 Ozeke KA100400102 Fraser KA100420101 Dixon GA100430101 Singh LA100477744 Smith P


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;

• Views can also be defined based on other views.CREATE VIEW smithloan

AS

SELECT *

FROM loan_names

WHERE member = 'Smith*';

• DROP VIEW - Remove an existing view

• DROP VIEW loan_names;


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 entryCreate Trigger dispAllEntrieson studentsfor insert asselect * from students


DROP TABLE

• Remove an existing table

DROP TABLE table_name;

• To eliminate the publisher table, you would use:

DROP TABLE publisher;

• To eliminate the student table, you would use:

DROP TABLE students


End of Data Definition Language


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. SELECT2. SELECT & FROM3. WHERE CLAUSE4. ORDER BY5. DISTINCT6. BETWEEN and LIKE7. IN and NOT IN8. Joining Tables9. Aliases for Tables10. More on Joins11. Examining the Joins12. Sub-Queries

13. INSERT14. CREATE TRIGGER15. DELETE16. UPDATE


• 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

DML OVERVIEW


SELECT

• 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‘• Getting all fields of all entries back:

select * from students• Finding Darryn

select * from students where firstName = ‘Darryn'


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


SELECT & FROM

• A simple example

SELECT bor_state

FROM limit;

BOR_STATE

1

2

3

4

5

• 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;


WHERE CLAUSE

SELECT *FROM bookWHERE now_price > 5;

• If we only wanted book details for the books with isbn '86007906', then the query would be:

SELECT *FROM bookWHERE isbn = '86007906';

• If we wanted book details for books with NOW_price 4.99 or 5.99,SELECT *FROM bookWHERE now_price = 4.99 OR now_price = 5.99;

• AND, OR & NOT can be used in WHERE statements.


ORDER BY• 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 publisherORDER BY pub_name;

Or ..SELECT *FROM bookWHERE pub_date > '1989'ORDER BY pub_date, title;

ISBNX PUB_CODE TITLE PUB_DATE NOW_PRICE

09946950 LEGD Contact 1990 4.99

55213703 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


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_noFROM reservation; gives:

BOR_NOB0000006B0000004B0000004B0000009B0000007B0000002B0000008B0000007

• 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:

BOR_NOB0000006B0000004B0000009B0000007B0000002B0000008


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 * use as usual?


IN and NOT IN

– 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?

• 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 ] ;


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?)

bor_nameSpawton PMajathia RMajathia RSmith PFraser FFraser FRizzo HSmith W


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.


• Supposing we had wanted, for all reservations, the bor_no and bor_name along with the title of each book.

BORROWER RESERVATION BOOK m m 1 1

We need to link all three tables

of by

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?

More on Joins


• Notice:

bor_no is in both reservation and borrower.

isbn is in both reservation and book.

• So … can you write the query?

• 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.

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;


Examining the Joins

• Notice how simple it is to write the syntax for the two joins.

BORROWER RESERVATION BOOK

br.bor_no = r.bor_no 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)


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);


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.


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')


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 entryCreate Trigger dispAllEntrieson studentsfor insert asselect * from students


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'


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 studentsset firstName = 'darryn', lastName='campbell'where studentID='u63773941'


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.

SQL_Data_Definition Domains Metadata XML

SQL Sub Queries SQL Groups SQL Data Definition Views

Key Relational and SQL Concepts (part 1 of 3)




End of Data Manipulation Language

Section 3SQL Overview1 HSQ - DATABASES & SQL And Franchise Colleges 3 SQL Overview By MANSHA NAWAZ.

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