SQL SQL Server : Overview SQL : Overview Types of SQL Database : Creation Tables : Creation & Manipulation Data : Creation & Manipulation Data : Retrieving using SQL

SQL : Overview Is the standard command set used to

communicate with the relational database management systems

Can do Creating databases, Creating tables, Querying and Manipulating data and granting access to the users

English like structure is by nature flexible

Types of SQL Commands SQL statements are divided into the following

categories Data Definition Language (DDL) Data Manipulation Language (DML) Data Query Language (DQL) Data Control Language (DCL) Data Administration Statements (DAS) Transaction Control Statements (TCS)

Data Definition Language Is used to create, alter and delete database

objects The commands used are

CREATE ALTER DROP

Data Manipulation Language Used to insert data into the database,

modify and delete the data in the database Three DML statements

INSERT UPDATE DELETE

Data Query Language This statement enables you to query one or

more tables to get the information commonly used SQL statements SQL has only one data query statement

SELECT

Data Control Language The DCL consists of commands that

control the user’s access to the database objects

The DCL is mainly related to the security issues

The DCL commands are GRANT - Giving access to the data REVOKE - Denying access to the data

Data Administration Statements DASs allow the user to perform audits and

analysis on operations within the database. Used to analyze the performance of the

system Data Administration commands are

START AUDIT STOP AUDIT

Transaction Control Statements TCSs are statements, which manage all the

changes made by the DML statements Some of the TCSs are

COMMIT ROLLBACK SAVEPOINT SET TRANSACTION

Databases Collection of related data and manipulation

of that data Can create database using SQL command

CREATE DATABASE databasename

Tables Are the basic building blocks in any

RDBMS contains rows and columns of data using DDL commands, we can create ,

alter and delete tables Creation of table includes the properties of

the columns

Create statementCREATE TABLE table-name

(column-1-definition

[,column-2-definition] …..

[,column-n-definition]

[,primary key (column name)]

[.alternate key (column name)]

[,Foreign key (column name) ]);

Column definition columnName data-type [NULL | NOT NULL

[WITH DEFAULT | UNIQUE]]

NULL - RDBMS insert a null in that column if the user does not specify a value

NOT NULL - column should have a value WITH DEFAULT - the RDBMS will substitute

the default values UNIQUE - no duplicate values will be allowed

Data types char(n) - represents a fixed length of string of ‘n’

characters where n>0 and is an integer varchar(n) - varying length string whose max

length is ‘n’ bit(n) - represents a fixed length string of exactly

‘n’ bits decimal(p, q) - represents a decimal number, ‘p’

digits and with decimal point ‘q’ digits from right

Data Types float(n) - represents the floating point

number int - represents a signed integer datetime - represents the date/time money - represents the currency

2nd form of CREATE CREATE TABLE new-table-name LIKE

table-name when a table is created from an existing

table only the structure is copied; the primary, alternate and foreign key definitions is not inherited

Modifying a Table An existing table can be modified by using

the ALTER TABLE statement ALTER TABLE table-name

ADD column definition ALTER TABLE table-name

Add CONSTRAINT constraint name

Primary key (column name)

Deleting a table An existing table can be deleted at any

time by using the DROP TABLE statement DROP TABLE table-name specified table is deleted from the system all the data for that table also will be

deleted

Inserting rows into a table INSERT INTO table-name

[[column [,column]….]]

values [literal[,literal]…]]; a single row is inserted into the table, having

specified columns INSERT INTO table-name

[[column [,column]….]]

subquery; the subquery is evaluated first and a copy of the

result(usually multiple rows) is inserted into the table

Updating fields in a row UPDATE table-name

SET column-name = expr

[WHERE condition] table-name : table for the data to be updated SET clause : the set of new values to be set WHERE clause : condition will be checked

and particular record gets updated

Deleting of data from the table DELETE FROM table-name

WHERE condition Depending on the condition the record will

be deleted from the table

SELECT statements SELECT - A keyword that tells the

database this command is a query. All queries begin with this word followed by a space

the select command simply instructs the database to retrieve information from a table

Different features applied to a simple statement All columns Qualified Retrieval Eliminating Duplicates Using Boolean(IN, BETWEEN, LIKE) Using Escape clause Computed values Involving nulls

All Columns SELECT * FROM Table-name

Qualified Retrieval SELECT * FROM table-name

WHERE condition can use all comparision operators (=, <>, <, >, <=,

>=) in the WHERE clause can contain multiple comparison with AND, OR,

NOT Eliminating Duplicates

SELECT DISTINCT column-name FROM table-name

Using Boolean Operators IN

SELECT * FROM table-name

WHERE column-name IN (val1, val2, val3…); BETWEEN

SELECT * FROM table-name

WHERE column-name BETWEEN val1 and val2 between is an inclusive operator values matching either of the boundary values

cause the predicate to be true

NOT BETWEEN SELECT * FROM table-name

WHERE column-name NOT BETWEEN val1 and val2

LIKE SELECT * FROM table-name

WHERE column-name LIKE ‘string%’ LIKE ‘_%’

Escape Sequence SELECT * FROM table-name

WHERE column-name LIKE ‘%\_%’

Computed Values SELECT column1, column2Expression

FROM table-name

WHERE condition NULLS

SELECT * FROM table-name

WHERE column-name IS NULL ORDER BY

SELECT * FROM table-name

ORDER BY column-name DESC