DATA BASE

Página 1

SQL is a language to operate databases; it includes database creation, deletion, fetching rows, modifying rows, etc. SQL is an ANSI (American National Standards Institute) standard language, but there are many different versions of the SQL language.

What is SQL?

SQL is Structured Query Language, which is a computer language for storing, manipulating and retrieving data stored in a relational database.

SQL is the standard language for Relational Database System. All the Relational Database Management Systems (RDMS) like MySQL, MS Access, Oracle, Sybase, Informix, Postgres and SQL Server use SQL as their standard database language.

Also, they are using different dialects, such as −

MS SQL Server using T-SQL,

Oracle using PL/SQL,

MS Access version of SQL is called JET SQL (native format) etc.

Why SQL?

SQL is widely popular because it offers the following advantages −

Allows users to access data in the relational database management systems.

Allows users to describe the data.

Allows users to define the data in a database and manipulate that data.

Allows to embed within other languages using SQL modules, libraries & pre-compilers.

Allows users to create and drop databases and tables.

Allows users to create view, stored procedure, functions in a database.

Allows users to set permissions on tables, procedures and views.

A Brief History of SQL

1970 − Dr. Edgar F. "Ted" Codd of IBM is known as the father of relational databases. He described a relational model for databases.

1974 − Structured Query Language appeared.

1978 − IBM worked to develop Codd's ideas and released a product named System/R.

1986 − IBM developed the first prototype of relational database and standardized by ANSI. The first relational database was released by Relational Software which later came to be known as Oracle.

SQL Process

When you are executing an SQL command for any RDBMS, the system determines the best way to carry out your request and SQL engine figures out how to interpret the task.

There are various components included in this process.

These components are −

Query Dispatcher

Optimization Engines

Classic Query Engine

SQL Query Engine, etc.

A classic query engine handles all the non-SQL queries, but a SQL query engine won't handle logical files.

Following is a simple diagram showing the SQL Architecture −

SQL Commands

The standard SQL commands to interact with relational databases are CREATE, SELECT, INSERT, UPDATE, DELETE and DROP. These commands can be classified into the following groups based on their nature −

DDL - Data Definition Language

Sr.No.Command & Description

1

CREATE

Creates a new table, a view of a table, or other object in the database.

2

ALTER

Modifies an existing database object, such as a table.

3

DROP

Deletes an entire table, a view of a table or other objects in the database.

DML - Data Manipulation Language

Sr.No.Command & Description

1

SELECT

Retrieves certain records from one or more tables.

2

INSERT

Creates a record.

3

UPDATE

Modifies records.

4

DELETE

Deletes records.

DCL - Data Control Language

Sr.No.Command & Description

1

GRANT

Gives a privilege to user.

2

REVOKE

Takes back privileges granted from user.

SQL - RDBMS Concepts

What is RDBMS?

RDBMS stands for Relational Database Management System. RDBMS is the basis for SQL, and for all modern database systems like MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access.

A Relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by E. F. Codd.

What is a table?

The data in an RDBMS is stored in database objects which are called as tables. This table is basically a collection of related data entries and it consists of numerous columns and rows.

Remember, a table is the most common and simplest form of data storage in a relational database. The following program is an example of a CUSTOMERS table −

+----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+

What is a field?

Every table is broken up into smaller entities called fields. The fields in the CUSTOMERS table consist of ID, NAME, AGE, ADDRESS and SALARY.

A field is a column in a table that is designed to maintain specific information about every record in the table.

What is a Record or a Row?

A record is also called as a row of data is each individual entry that exists in a table. For example, there are 7 records in the above CUSTOMERS table. Following is a single row of data or record in the CUSTOMERS table −

+----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | +----+----------+-----+-----------+----------+

A record is a horizontal entity in a table.

What is a column?

A column is a vertical entity in a table that contains all information associated with a specific field in a table.

For example, a column in the CUSTOMERS table is ADDRESS, which represents location description and would be as shown below −

+-----------+ | ADDRESS | +-----------+ | Ahmedabad | | Delhi | | Kota | | Mumbai | | Bhopal | | MP | | Indore | +----+------+

What is a NULL value?

A NULL value in a table is a value in a field that appears to be blank, which means a field with a NULL value is a field with no value.

It is very important to understand that a NULL value is different than a zero value or a field that contains spaces. A field with a NULL value is the one that has been left blank during a record creation.

SQL Constraints

Constraints are the rules enforced on data columns on a table. These are used to limit the type of data that can go into a table. This ensures the accuracy and reliability of the data in the database.

Constraints can either be column level or table level. Column level constraints are applied only to one column whereas, table level constraints are applied to the entire table.

Following are some of the most commonly used constraints available in SQL −

NOT NULL Constraint − Ensures that a column cannot have a NULL value.

DEFAULT Constraint − Provides a default value for a column when none is specified.

UNIQUE Constraint − Ensures that all the values in a column are different.

PRIMARY Key − Uniquely identifies each row/record in a database table.

FOREIGN Key − Uniquely identifies a row/record in any another database table.

CHECK Constraint − The CHECK constraint ensures that all values in a column satisfy certain conditions.

INDEX − Used to create and retrieve data from the database very quickly.

Data Integrity

The following categories of data integrity exist with each RDBMS −

Entity Integrity − There are no duplicate rows in a table.

Domain Integrity − Enforces valid entries for a given column by restricting the type, the format, or the range of values.

Referential integrity − Rows cannot be deleted, which are used by other records.

User-Defined Integrity − Enforces some specific business rules that do not fall into entity, domain or referential integrity.

Database Normalization

Database normalization is the process of efficiently organizing data in a database. There are two reasons of this normalization process −

Eliminating redundant data, for example, storing the same data in more than one table.

Ensuring data dependencies make sense.

Both these reasons are worthy goals as they reduce the amount of space a database consumes and ensures that data is logically stored. Normalization consists of a series of guidelines that help guide you in creating a good database structure.

Normalization guidelines are divided into normal forms; think of a form as the format or the way a database structure is laid out. The aim of normal forms is to organize the database structure, so that it complies with the rules of first normal form, then second normal form and finally the third normal form.

It is your choice to take it further and go to the fourth normal form, fifth normal form and so on, but in general, the third normal form is more than enough.

First Normal Form (1NF)

Second Normal Form (2NF)

Third Normal Form (3NF)

SQL - RDBMS Databases

There are many popular RDBMS available to work with. This tutorial gives a brief overview of some of the most popular RDBMS’s. This would help you to compare their basic features.

MySQL

MySQL is an open source SQL database, which is developed by a Swedish company – MySQL AB. MySQL is pronounced as "my ess-que-ell," in contrast with SQL, pronounced "sequel."

MySQL is supporting many different platforms including Microsoft Windows, the major Linux distributions, UNIX, and Mac OS X.

MySQL has free and paid versions, depending on its usage (non-commercial/commercial) and features. MySQL comes with a very fast, multi-threaded, multi-user and robust SQL database server.

History

Development of MySQL by Michael Widenius & David Axmark beginning in 1994.

First internal release on 23rd May 1995.

Windows Version was released on the 8th January 1998 for Windows 95 and NT.

Version 3.23: beta from June 2000, production release January 2001.

Version 4.0: beta from August 2002, production release March 2003 (unions).

Version 4.01: beta from August 2003, Jyoti adopts MySQL for database tracking.

Version 4.1: beta from June 2004, production release October 2004.

Version 5.0: beta from March 2005, production release October 2005.

Sun Microsystems acquired MySQL AB on the 26th February 2008.

Version 5.1: production release 27th November 2008.

Features

High Performance.

High Availability.

Scalability and Flexibility Run anything.

Robust Transactional Support.

Web and Data Warehouse Strengths.

Strong Data Protection.

Comprehensive Application Development.

Management Ease.

Open Source Freedom and 24 x 7 Support.

Lowest Total Cost of Ownership.

MS SQL Server

MS SQL Server is a Relational Database Management System developed by Microsoft Inc. Its primary query languages are −

T-SQL

ANSI SQL

History

1987 - Sybase releases SQL Server for UNIX.

1988 - Microsoft, Sybase, and Aston-Tate port SQL Server to OS/2.

1989 - Microsoft, Sybase, and Aston-Tate release SQL Server 1.0 for OS/2.

1990 - SQL Server 1.1 is released with support for Windows 3.0 clients.

Aston - Tate drops out of SQL Server development.

2000 - Microsoft releases SQL Server 2000.

2001 - Microsoft releases XML for SQL Server Web Release 1 (download).

2002 - Microsoft releases SQLXML 2.0 (renamed from XML for SQL Server).

2002 - Microsoft releases SQLXML 3.0.

2005 - Microsoft releases SQL Server 2005 on November 7th, 2005.

Features

High Performance

High Availability

Database mirroring

Database snapshots

CLR integration

Service Broker

DDL triggers

Ranking functions

Row version-based isolation levels

XML integration

TRY...CATCH

Database Mail

ORACLE

It is a very large multi-user based database management system. Oracle is a relational database management system developed by 'Oracle Corporation'.

Oracle works to efficiently manage its resources, a database of information among the multiple clients requesting and sending data in the network.

It is an excellent database server choice for client/server computing. Oracle supports all major operating systems for both clients and servers, including MSDOS, NetWare, UnixWare, OS/2 and most UNIX flavors.

History

Oracle began in 1977 and celebrating its 32 wonderful years in the industry (from 1977 to 2009).

1977 - Larry Ellison, Bob Miner and Ed Oates founded Software Development Laboratories to undertake development work.

1979 - Version 2.0 of Oracle was released and it became first commercial relational database and first SQL database. The company changed its name to Relational Software Inc. (RSI).

1981 - RSI started developing tools for Oracle.

1982 - RSI was renamed to Oracle Corporation.

1983 - Oracle released version 3.0, rewritten in C language and ran on multiple platforms.

1984 - Oracle version 4.0 was released. It contained features like concurrency control - multi-version read consistency, etc.

1985 - Oracle version 4.0 was released. It contained features like concurrency control - multi-version read consistency, etc.

2007 - Oracle released Oracle11g. The new version focused on better partitioning, easy migration, etc.

Features

Concurrency

Read Consistency

Locking Mechanisms

Quiesce Database

Portability

Self-managing database

SQL*Plus

ASM

Scheduler

Resource Manager

Data Warehousing

Materialized views

Bitmap indexes

Table compression

Parallel Execution

Analytic SQL

Data mining

Partitioning

MS ACCESS

This is one of the most popular Microsoft products. Microsoft Access is an entry-level database management software. MS Access database is not only inexpensive but also a powerful database for small-scale projects.

MS Access uses the Jet database engine, which utilizes a specific SQL language dialect (sometimes referred to as Jet SQL).

MS Access comes with the professional edition of MS Office package. MS Access has easyto-use intuitive graphical interface.

1992 - Access version 1.0 was released.

1993 - Access 1.1 released to improve compatibility with inclusion the Access Basic programming language.

The most significant transition was from Access 97 to Access 2000.

2007 - Access 2007, a new database format was introduced ACCDB which supports complex data types such as multi valued and attachment fields.

Features

Users can create tables, queries, forms and reports and connect them together with macros.

Option of importing and exporting the data to many formats including Excel, Outlook, ASCII, dBase, Paradox, FoxPro, SQL Server, Oracle, ODBC, etc.

There is also the Jet Database format (MDB or ACCDB in Access 2007), which can contain the application and data in one file. This makes it very convenient to distribute the entire application to another user, who can run it in disconnected environments.

Microsoft Access offers parameterized queries. These queries and Access tables can be referenced from other programs like VB6 and .NET through DAO or ADO.

The desktop editions of Microsoft SQL Server can be used with Access as an alternative to the Jet Database Engine.

Microsoft Access is a file server-based database. Unlike the client-server relational database management systems (RDBMS), Microsoft Access does not implement database triggers, stored procedures or transaction logging.

SQL - Syntax

SQL is followed by a unique set of rules and guidelines called Syntax. This tutorial gives you a quick start with SQL by listing all the basic SQL Syntax.

All the SQL statements start with any of the keywords like SELECT, INSERT, UPDATE, DELETE, ALTER, DROP, CREATE, USE, SHOW and all the statements end with a semicolon (;).

The most important point to be noted here is that SQL is case insensitive, which means SELECT and select have same meaning in SQL statements. Whereas, MySQL makes difference in table names. So, if you are working with MySQL, then you need to give table names as they exist in the database.

Various Syntax in SQL

All the examples given in this tutorial have been tested with a MySQL server.

SQL SELECT Statement

SELECT column1, column2....columnN FROM table_name;

SQL DISTINCT Clause

SELECT DISTINCT column1, column2....columnN FROM table_name;

SQL WHERE Clause

SELECT column1, column2....columnN FROM table_name WHERE CONDITION;

SQL AND/OR Clause

SELECT column1, column2....columnN FROM table_name WHERE CONDITION-1 {AND|OR} CONDITION-2;

SQL IN Clause

SELECT column1, column2....columnN FROM table_name WHERE column_name IN (val-1, val-2,...val-N);

SQL BETWEEN Clause

SELECT column1, column2....columnN FROM table_name WHERE column_name BETWEEN val-1 AND val-2;

SQL LIKE Clause

SELECT column1, column2....columnN FROM table_name WHERE column_name LIKE { PATTERN };

SQL ORDER BY Clause

SELECT column1, column2....columnN FROM table_name WHERE CONDITION ORDER BY column_name {ASC|DESC};

SQL GROUP BY Clause

SELECT SUM(column_name) FROM table_name WHERE CONDITION GROUP BY column_name;

SQL COUNT Clause

SELECT COUNT(column_name) FROM table_name WHERE CONDITION;

SQL HAVING Clause

SELECT SUM(column_name) FROM table_name WHERE CONDITION GROUP BY column_name HAVING (arithematic function condition);

SQL CREATE TABLE Statement

CREATE TABLE table_name( column1 datatype, column2 datatype, column3 datatype, ..... columnN datatype, PRIMARY KEY( one or more columns ) );

SQL DROP TABLE Statement

DROP TABLE table_name;

SQL CREATE INDEX Statement

CREATE UNIQUE INDEX index_name ON table_name ( column1, column2,...columnN);

SQL DROP INDEX Statement

ALTER TABLE table_name DROP INDEX index_name;

SQL DESC Statement

DESC table_name;

SQL TRUNCATE TABLE Statement

TRUNCATE TABLE table_name;

SQL ALTER TABLE Statement

ALTER TABLE table_name {ADD|DROP|MODIFY} column_name {data_ype};

SQL ALTER TABLE Statement (Rename)

ALTER TABLE table_name RENAME TO new_table_name;

SQL INSERT INTO Statement

INSERT INTO table_name( column1, column2....columnN) VALUES ( value1, value2....valueN);

SQL UPDATE Statement

UPDATE table_name SET column1 = value1, column2 = value2....columnN=valueN [ WHERE CONDITION ];

SQL DELETE Statement

DELETE FROM table_name WHERE {CONDITION};

SQL CREATE DATABASE Statement

CREATE DATABASE database_name;

SQL DROP DATABASE Statement

DROP DATABASE database_name;

SQL USE Statement

USE database_name;

SQL COMMIT Statement

COMMIT;

SQL ROLLBACK Statement

ROLLBACK;

SQL - Data Types

SQL Data Type is an attribute that specifies the type of data of any object. Each column, variable and expression has a related data type in SQL. You can use these data types while creating your tables. You can choose a data type for a table column based on your requirement.

SQL Server offers six categories of data types for your use which are listed below −

Exact Numeric Data Types

DATA TYPEFROMTO

bigint-9,223,372,036,854,775,8089,223,372,036,854,775,807

int-2,147,483,6482,147,483,647

smallint-32,76832,767

tinyint0255

bit01

decimal-10^38 +110^38 -1

numeric-10^38 +110^38 -1

money-922,337,203,685,477.5808+922,337,203,685,477.5807

smallmoney-214,748.3648+214,748.3647

Approximate Numeric Data Types

DATA TYPEFROMTO

float-1.79E + 3081.79E + 308

real-3.40E + 383.40E + 38

Date and Time Data Types

DATA TYPEFROMTO

datetimeJan 1, 1753Dec 31, 9999

smalldatetimeJan 1, 1900Jun 6, 2079

dateStores a date like June 30, 1991

timeStores a time of day like 12:30 P.M.

Note − Here, datetime has 3.33 milliseconds accuracy where as smalldatetime has 1 minute accuracy.

Character Strings Data Types

Sr.No.DATA TYPE & Description

1

char

Maximum length of 8,000 characters.( Fixed length non-Unicode characters)

2

varchar

Maximum of 8,000 characters.(Variable-length non-Unicode data).

3

varchar(max)

Maximum length of 2E + 31 characters, Variable-length non-Unicode data (SQL Server 2005 only).

4

text

Variable-length non-Unicode data with a maximum length of 2,147,483,647 characters.

Unicode Character Strings Data Types

Sr.No.DATA TYPE & Description

1

nchar

Maximum length of 4,000 characters.( Fixed length Unicode)

2

nvarchar

Maximum length of 4,000 characters.(Variable length Unicode)

3

nvarchar(max)

Maximum length of 2E + 31 characters (SQL Server 2005 only).( Variable length Unicode)

4

ntext

Maximum length of 1,073,741,823 characters. ( Variable length Unicode )

Binary Data Types

Sr.No.DATA TYPE & Description

1

binary

Maximum length of 8,000 bytes(Fixed-length binary data )

2

varbinary

Maximum length of 8,000 bytes.(Variable length binary data)

3

varbinary(max)

Maximum length of 2E + 31 bytes (SQL Server 2005 only). ( Variable length Binary data)

4

image

Maximum length of 2,147,483,647 bytes. ( Variable length Binary Data)

Misc Data Types

Sr.No.DATA TYPE & Description

1

sql_variant

Stores values of various SQL Server-supported data types, except text, ntext, and timestamp.

2

timestamp

Stores a database-wide unique number that gets updated every time a row gets updated

3

uniqueidentifier

Stores a globally unique identifier (GUID)

4

xml

Stores XML data. You can store xml instances in a column or a variable (SQL Server 2005 only).

5

cursor

Reference to a cursor object

6

table

Stores a result set for later processing

SQL - Operators

What is an Operator in SQL?

An operator is a reserved word or a character used primarily in an SQL statement's WHERE clause to perform operation(s), such as comparisons and arithmetic operations. These Operators are used to specify conditions in an SQL statement and to serve as conjunctions for multiple conditions in a statement.

Arithmetic operators

Comparison operators

Logical operators

Operators used to negate conditions

SQL Arithmetic Operators

Assume 'variable a' holds 10 and 'variable b' holds 20, then −

Show Examples

OperatorDescriptionExample

+ (Addition)Adds values on either side of the operator.a + b will give 30

- (Subtraction)Subtracts right hand operand from left hand operand.a - b will give -10

* (Multiplication)Multiplies values on either side of the operator.a * b will give 200

/ (Division)Divides left hand operand by right hand operand.b / a will give 2

% (Modulus)Divides left hand operand by right hand operand and returns remainder.b % a will give 0

SQL Comparison Operators

Assume 'variable a' holds 10 and 'variable b' holds 20, then −

Show Examples

OperatorDescriptionExample

=Checks if the values of two operands are equal or not, if yes then condition becomes true.(a = b) is not true.

!=Checks if the values of two operands are equal or not, if values are not equal then condition becomes true.(a != b) is true.

<>Checks if the values of two operands are equal or not, if values are not equal then condition becomes true.(a <> b) is true.

>Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true.(a > b) is not true.

>=Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true.(a >= b) is not true.

<=Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true.(a <= b) is true.

!

!>Checks if the value of left operand is not greater than the value of right operand, if yes then condition becomes true.(a !> b) is true.

SQL Logical Operators

Here is a list of all the logical operators available in SQL.

Show Examples

Sr.No.Operator & Description

1

ALL

The ALL operator is used to compare a value to all values in another value set.

2

AND

The AND operator allows the existence of multiple conditions in an SQL statement's WHERE clause.

3

ANY

The ANY operator is used to compare a value to any applicable value in the list as per the condition.

4

BETWEEN

The BETWEEN operator is used to search for values that are within a set of values, given the minimum value and the maximum value.

5

EXISTS

The EXISTS operator is used to search for the presence of a row in a specified table that meets a certain criterion.

6

IN

The IN operator is used to compare a value to a list of literal values that have been specified.

7

LIKE

The LIKE operator is used to compare a value to similar values using wildcard operators.

8

NOT

The NOT operator reverses the meaning of the logical operator with which it is used. Eg: NOT EXISTS, NOT BETWEEN, NOT IN, etc. This is a negate operator.

9

OR

The OR operator is used to combine multiple conditions in an SQL statement's WHERE clause.

10

IS NULL

The NULL operator is used to compare a value with a NULL value.

11

UNIQUE

The UNIQUE operator searches every row of a specified table for uniqueness (no duplicates).