SQL by Nadia

8/3/2019 SQL by Nadia

http://slidepdf.com/reader/full/sql-by-nadia 1/57

Prepared By Ms.Nadia Shah 1

Design and ImplementationDesign and ImplementationBy Lect: Mst. Nadia ShahBy Lect: Mst. Nadia Shah




An Overview of An Overview of

SQLSQL

SQL stands for SQL stands for SStructuredtructured QQueryuery LLanguage.anguage.

It is the most commonly used relationalIt is the most commonly used relational

database language today.database language today.

SQL works with a variety of different fourthSQL works with a variety of different fourth--

generation (4GL) programming languages,generation (4GL) programming languages,

such as Visual Basic.such as Visual Basic.




SQL is used for:SQL is used for:

Data ManipulationData Manipulation

Data DefinitionData Definition Data AdministrationData Administration

All are expressed as an SQL statement All are expressed as an SQL statement

or command.or command.




SQLSQL

RequirementsRequirements

SQL is a free form language so there is noSQL is a free form language so there is no

limit to the number of words per line or fixedlimit to the number of words per line or fixed

line break.line break.

Syntax statements, words or phrases areSyntax statements, words or phrases are

always in lower case; keywords are inalways in lower case; keywords are in

uppercase.uppercase. Not all versions are case sensitive! Not all versions are case sensitive!




SQL is a Relational DatabaseSQL is a Relational Database

Represent all info in database as tablesRepresent all info in database as tables

Use one highUse one high--level language for structuring,level language for structuring,querying, and changing info in the databasequerying, and changing info in the database

Support the main relational operationsSupport the main relational operations

Support alternate ways of looking at data inSupport alternate ways of looking at data intablestables

Support Mechanisms for integrity, authorization,Support Mechanisms for integrity, authorization,transactions, and recoverytransactions, and recovery

A Fully Relational Database Management System must:A Fully Relational Database Management System must:




DesignDesign

SQL represents all information in the

form of tables

Supports three relational operations:

selection, projection, and join. These

are for specifying exactly what data you

want to display or use

S Q L




SQL Data Manipulation Language

(DML)

SQL (Structured Query Language) is a syntax forexecuting queries. But the SQL language also

includes a syntax to update, insert, and deleterecords.These query and update commands together formthe Data Manipulation Language (DML) part of SQL:

SELECT-

extracts data from a database tableUPDATE - updates data in a database tableDELETE - deletes data from a database tableINSERT INTO - inserts new data into adatabase table




SQL Data Definition Language

(DDL) The Data Definition Language (DDL) part of SQL permits

database tables to be created or deleted. We can also defineindexes (keys), specify links between tables, and impose

constraints between database tables. The most important DDL statements in SQL are:

CREATE TABLE - creates a new database table

ALTER TABLE - alters (changes) a database table

DROP TABLE - deletes a database table

CREATE INDEX - creates an index (search key)

DROP INDEX - deletes an index




Using SQLUsing SQL

SQL statements can be embedded into a programSQL statements can be embedded into a program

( Visual Basic, MS Access)( Visual Basic, MS Access)

OROR

SQL statements can be entered directly at theSQL statements can be entered directly at the

command prompt of the SQL software beingcommand prompt of the SQL software being

used (such as mySQL)used (such as mySQL)




Using SQLUsing SQL

To begin, you must first CREATE a database usingTo begin, you must first CREATE a database using

the following SQL statement:the following SQL statement:

CREATE DATABASE database_nameCREATE DATABASE database_name




Using SQLUsing SQL

To create a table in the current database,

use the CREATE TABLE keyword

CREATE TABLE authorsCREATE TABLE authors(auth_id int(9) not null,(auth_id int(9) not null,auth_name char(40) not null)auth_name char(40) not null)

auth_id auth_name

(9 digit int) (40 char string)




Data InputData Input

Putting data into a table is accomplishedPutting data into a table is accomplishedusing the keywordusing the keyword INSERT

pub_id pub_name address state

0736 New Age Books 1 1st Street MA

0987 Binnet & Hardley 2 2nd Street DC

1120 Algodata Infosys 3 3rd Street CA

Table is updated with new informationTable is updated with new information

INSERT INTO publishersINSERT INTO publishers

VALUES (¶0010·, ¶pragmatics·, ¶4 4VALUES (¶0010·, ¶pragmatics·, ¶4 4thth Ln·, ¶chicago·, ¶il·)Ln·, ¶chicago·, ¶il·)


0010 Pragmatics 4 4th Ln IL


0987 Binnet & Hardley 2 2

nd

Street DC1120 Algodata Infosys 3 3rd Street CA

Keyword

Variable




Using SQLUsing SQL

DROP TABLE authorsDROP TABLE authors

auth_id auth_name auth_city auth_state

123456789 Jane Doe Dearborn MI

000000001 John Smith Taylor MI

The DROP statement is also used to delete

an entire database & Tables as well.

DROP removed the Table and returned

the memory to system




Rows

describe the

Occurrence of an Entity

Table DesignTable Design

Name Address

Jane Doe 123 Main Street

John Smith 456 Second Street

Mary Poe 789 Third Ave

Columns describe one

characteristic of the entity




Basic structureBasic structure

of an SQL queryof an SQL query

General

Structure

SELECT, ALL / DISTINCT, *,

AS, FROM, WHERE

Comparison IN, BETWEEN, LIKE "% _"

Grouping GROUP BY, HAVING,

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

Display Order ORDER BY, ASC / DESC

LogicalOperators

AND, OR, NOT

Output INTO TABLE / CURSOR

TO FILE [ADDITIVE], TO PRINTER, TO SCREEN

Union UNION




SQL The SELECT Statement

The SELECT statement is used to select data

from a table. The tabular result is stored in a

result table (called the result-set). Syntax

± SELECT column_name(s)

± FROM table_name




Using SQLUsing SQL

SELECT auth_name, auth_citySELECT auth_name, auth_city

FROM publishersFROM publishers


123456789 Jane Doe Dearborn MI

000000001 John Smith Taylor MI

auth_name auth_city

Jane Doe Dearborn

John Smith Taylor

If you only want to display the author¶s

name and city from the following table:




Data Retrieval (Queries)Data Retrieval (Queries)

Queries search the database, fetch info,Queries search the database, fetch info,and display it. This is done using theand display it. This is done using thekeywordkeyword SELECT

SELECT * FROM publishersSELECT * FROM publisherspub_id pub_name address state




TheThe ** Operator asks for every column inOperator asks for every column in

the table.the table.




Using the DISTINCT keyword To select ALL values from the column named

"Company" we use a SELECT statement like this:

SELECT DISTINCT Company

FROM OrdersOrders

Company OrderNumber

Sega 3412

W3Schools 2312

Trio 4678

W3Schools 6798

Company

Sega

W3Schools

Trio




Data Retrieval (WHERE)Data Retrieval (WHERE)

Queries can be more specific with a few moreQueries can be more specific with a few morelines. Operator arelines. Operator are =, <> ,> ,< , >= ,<=, =, <> ,> ,< , >= ,<=,

BETWEEN, LIKE, IN are used in where clauseBETWEEN, LIKE, IN are used in where clause





Only publishers in CA are displayedOnly publishers in CA are displayed

SELECT *SELECT *from publishersfrom publishers

where state = ¶CA·where state = ¶CA·




Comparison Operators




SELECT Command Involving a

Comparison




Compound Conditions

Compound conditions

± Formed by connecting two or more simple

conditions ± Uses AND, OR, and NOT operators

AND: all conditions must be true

OR: any one of conditions is true

NOT: reverses the truth of the originalcondition




SELECT Command Involving an

AND Condition




SELECT Command Involving an

OR Condition





NOT Condition




Use of BETWEEN

BETWEEN operator

± Not an essential feature

± Can arrive at same answer without it using AND

± Does make certain SELECT commands

simpler





BETWEEN Condition




Using an Alias ³AS´

Tables listed in the FROM clause can be

given an alternative name ± Create alias by typing the name of the table

± Press the space bar

± Type the name of the alias (no commas or periods are necessary)




Using LIKE The following SQL statement will return persons

with first names that start with an 'O':

SELECT * FROM Persons

WHERE FirstName LIKE 'O%'

The following SQL statement will return persons

with first names that end with an 'a':

SELECT * FROM Persons

WHERE FirstName LIKE '%a'




Using Functions

SQL has functions to calculate

± Sums

± Averages

± Counts

± Maximum values

± Minimum values




SQL Functions




SELECT Command to Count

Rows




SELECT Command to Calculate a

COUNT and a SUM




Using AVG, MAX, and MIN

AVG, MAX and MIN functions are similar

to the SUM

SUM, AVG, MAX and MIN functions

ignore (eliminate) null values

± Null values can cause strange results whencalculated




SELECT Command With Several

Functions




Use of ORDER BY

Use the ORDER BY command to list

data in a specific order The column on which data is to be sorted

is called a sort key or simply key




ORDER BY

ORDER BY clause is used for data is in

ASC or DESC order

SELECT * FROM mytable

ORDER BY salary ASC

OR

ORDER BY salary DESC




SQL Query Clauses andOperators




Types of TablesTypes of Tables

U ser Tables:U ser Tables: contain information that iscontain information that isthe database management systemthe database management system

System Tables:System Tables: contain the databasecontain the database

description, kept up to date by DBMSdescription, kept up to date by DBMSitself itself

There are two types of tables which make upThere are two types of tables which make up

a relational database in SQLa relational database in SQL

Relation Table

Tuple Row

Attribute Column




Using SQLUsing SQL

UPDATE authorsUPDATE authorsSET auth_name=¶hello·SET auth_name=¶hello·


123456789 Jane Doe Dearborn MI000000001 John Smith Taylor MI

To Update information in a database use

the UPDATE keyword

HelloHello

Sets all auth_name fields to helloSets all auth_name fields to hello




Using SQLUsing SQL

ALTER TABLE authorsALTER TABLE authorsADD birth_date datetime nullADD birth_date datetime null



To change a table in a database use ALTER

TABLE. ADD adds a characteristic.

ADD puts a new column in the table

called birth_date

birth_date

.

.

Type Initializer




Using SQLUsing SQL

ALTER TABLE authorsALTER TABLE authorsDROP birth_dateDROP birth_date



To delete a column or row, use the

keyword DROP

DROP removed the birth_date

characteristic from the table

auth_state

.

.




Using SQLUsing SQL

DELETE from authorsDELETE from authorsWHERE auth_name=¶John Smith·WHERE auth_name=¶John Smith·



To delete data from a table, use

the DELETE statement:




Using GROUP BY

GROUP BY command allows data to be

grouped in a particular order Statistics are calculated on the groups




Grouping Column




Query Using a HAVING Clause




HAVING vs. WHERE

WHERE clause limits rows

HAVING clause limits groups




Joining Two Tables

JOINS

Two methods

± Find rows in the two tables that haveidentical values in matching columns

and

± Use the appropriate conditions in the

WHERE clause




Multiple Tables:Multiple Tables:

SQL provides a convenient operation toSQL provides a convenient operation to

retrieve information from multiple tables.retrieve information from multiple tables.

ThisThis operationoperation isis calledcalled join join..

TheThe join join operationoperation willwill combinecombine thethe tablestables intointo

oneone largelarge tabletable withwith allall possible possible combinationscombinations

(Math(Math:: CartesianCartesian Product),Product), andand thenthen itit willwill filter filter

thethe rowsrows of of thisthis combinedcombined tabletable toto yieldyield usefulusefulinformationinformation..




SQL Joins

Joins are used to combine the contents of two or moretables and produce a result set into a single table thatincorporates rows and columns from each table.Tables are typically joined using data that they have

in common.

Join conditions can be specified in either the FROMor WHERE clauses, specifying them in the FROMclause is recommended. WHERE and HAVINGclauses can also contain search conditions to further filter the rows selected by the join conditions.




Types of joins

1. Equi joins

i. Inner join

ii. Outer join

a. Left outer join or left joiniii. Right outer join or right join

a. Full outer join or full join

iv. Cross join

v. Self join

2. Non equi joins.




Equi joins

In equi joins we use equality operator like =

It returns all the columns in both tables, and returns onlythe rows for which there is an equal value in the joincolumn.

Both the tables have a common column .

Examples of equi joins

± Inner join

± Outer join

± Cross join

± Self join

Inner join




Inner join

An inner join is a join in which the values in the columns being joined arecompared using a comparison operator

Inner joins use a comparison operator to match rows from two tables basedon the values in common columns from each table.

An INNER JOIN query returns one row for each pair or matching rows inthe tables being joined.

The result set of the inner join contains rows having the matched value of thecommon column.

syntax:-

( SELECT * FROM authors INNER JOIN publishers ON authors. city =

publishers. city )Where authors and publishers are the tables and city is the common columnin both the tables.




Outer join

In case of inner joins the result set contains only those rows which are

having matched values in common column ,but in case of outer join theresult set contains the unmatched value of the common column.

Types of outer joins

± Left outer join

± Right outer join

± Full outer join

Syntax :-

( SELECT * FROM authors OUTER JOIN publishers ON authors.city = publishers. city )

Where authors and publishers are the tables and city is the commoncolumn in both the tables.




Outer Join

LEFT JOIN or LEFT OUTER JOIN

The result set of a left outer join includes all the rows from the left table

specified in the LEFT OUTER clause, not just the ones in which the joinedcolumns match. When a row in the left table has no matching rows in the righttable, the associated result set row contains null values for all select listcolumns coming from the right table.

R IGHT JOIN or R IGHT OUTER JOIN.

A right outer join is the reverse of a left outer join. All rows from the right table

are returned. Null values are returned for the left table any time a right tablerow has no matching row in the left table.

FULL JOIN or FULL OUTER JOIN.

full outer join returns all rows in both the left and right tables. Any time a rowhas no match in the other table, the select list columns from the other tablecontain null values. When there is a match between the tables, the entire resultset row contains data values from the base tables.

SELECT customer.firstname, customer.lastname, purchases.item

FROM customer_info Outer Join purchases

ON customer.customer_no = purchases.customer_no;



P d B M N di Sh h 57

References

³The Practical SQL Handbook´, Third

Edition, Bowman.

SQL by Nadia

Documents

Transcript of SQL by Nadia