SQL Lesson1

8/9/2019 SQL Lesson1

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SQLSQL


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What is SQL?What is SQL?

y SQL stands for Structured Query

Language

y SQL lets you access and manipulate

databases

y SQL is an ANSI (American National

Standards Institute) standard


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What Can SQL do?What Can SQL do?

y SQL can execute queries against a databasey SQL can retrieve data from a database

y SQL can insert records in a databasey SQL can update records in a databasey SQL can delete records from a databasey SQL can create new databasesy SQL can create new tables in a databasey SQL can create stored procedures in a

databasey SQL can create views in a database

y SQL can set permissions on tables,procedures, and views


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SQL is a StandardSQL is a Standard

yAlthough SQL is an ANSI (AmericanNational Standards Institute) standard,there are many different versions of theSQL language.

y However, to be compliant with the ANSIstandard, they all support at least themajor commands (such as SELECT,UPDATE, DELETE, INSERT, WHERE) in

a similar manner.y Note: Most of the SQL database

programs also have their own proprietaryextensions in addition to the SQLstandard!


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Using SQL in Your Web SiteUsing SQL in Your Web Site

y To build a web site that shows some

data from a database, you will need

the following:

yAn RDBMS database program (i.e.

MS Access, SQL Server, MySQL)

yA server-side scripting language, like

PHP or ASPy SQL

y HTML / CSS


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RDBMSRDBMS

y RDBMS stands for Relational DatabaseManagement System.

y RDBMS is the basis for SQL, and for all

modern database systems like MS SQLServer, IBM DB2, Oracle, MySQL, andMicrosoft Access.

y The data in RDBMS is stored in

database objects called tables.yA table is a collections of related data

entries and it consists of columns androws.


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Database TablesDatabase Tables

The table above contains three records (one for each person) and

five columns (P_Id, LastName, FirstName, Address, and City).


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SQLStatementsSQLStatements

yMost of the actions you need to

perform on a database are done with

SQL statements.

y The following SQL statement will

select all the records in the "Persons"

table:

y SELECT * FROM Personsy In this tutorial we will teach you all

about the different SQL statements.


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SQLDML and DDLSQLDML and DDLy SQL can be divided into two parts: The Data Manipulation Language

(DML) and the Data Definition Language (DDL).

y The query and update commands form the DML part of SQL:

SELECT - extracts data from a database

UPDATE - updates data in a database

DELETE - deletes data from a database

INSERT INTO - inserts new data into a database

y The DDL part of SQL permits database tables to be created ordeleted. It also define indexes (keys), specify links between tables,and impose constraints between tables. The most important DDLstatements in SQL are:

CREATEDATABASE - creates a new database

ALTERDATABASE - modifies a database

CREATE TABLE - creates a new table ALTER TABLE - modifies a table

DROP TABLE - deletes a table

CREATEINDEX - creates an index (search key)

DROPINDEX - deletes an index


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The SQLSELECT StatementThe SQLSELECT Statement

y The SELECT statement is used to

select data from a database.

y The result is stored in a result table,

called the result-set.

y SQLSELECT Syntax

SELECT column_name(s)

FROM table_name and SELECT * FROM table_name


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The SQLSELECT DISTINCTThe SQLSELECT DISTINCT

StatementStatementy In a table, some of the columns may

contain duplicate values. This is not aproblem, however, sometimes you will

want to list only the different (distinct)values in a table.

y The DISTINCT keyword can be usedto return only distinct (different)

values.y SQLSELECT DISTINCT Syntax

SELECT DISTINCT column_name(s)FROM table_name


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The WHERE ClauseThe WHERE Clause

y The WHERE clause is used to extract

only those records that fulfill a

specified criterion.

y SQL WHERESyntax

SELECT column_name(s)

FROM table_name

WHERE column_name operator value


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WHERE Clause ExampleWHERE Clause Example


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Quotes Around Text FieldsQuotes Around Text Fieldsy SQL uses single quotes around text values (most database

systems will also accept double quotes).

y Although, numeric values should not be enclosed in quotes.

y For text values:

This is correct:

SELECT * FROM Persons WHERE FirstName='Tove'

This is wrong:

SELECT * FROM Persons WHERE FirstName=Tove For numericvalues:

This is correct:

SELECT * FROM Persons WHERE Year=1965

This is wrong:

SELECT * FROM Persons WHERE Year='1965'


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OperatorsAllowed in theOperatorsAllowed in the

WHERE ClauseWHERE Clause

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SQL Lesson1