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ABOUT THE TUTORIAL

This tutorial will give you a quick start to SQL. It covers most of the topics required for a basic understanding of SQL and to get a feel of how it works.

SQL is a database computer language designed for the retrieval and management of data in a relational database. SQL stands for Structured Query Language.             

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

     SQL is an interface between a human and a database.

Why SQL required? 

SQL is one of the most important inventions in the software engineering world, equally important to the invention of Internet. Most of the Web applications today store their data in Relational Databases and SQL is the ubiquitous language that is used to and many more things. 

  1. Create the tables and relationships between them.
  2. query data
  3. update data
  4. delete data 

What is Database?

A database is a collection of information that is organized so that it can easily be accessed, managed, and updated. 

An SQL database is a relational database that makes uses of the Structured Query Language (SQL) to query or communicate with the database.

A database is simply a collection of organized information, usually as a set of related lists of similar entries. The data is often organized so that it is easily accessible.

  • The following are examples of databases that we use often:

       – address book – dictionary – telephone book

A cylindrical structure is used to display the image of a database.

A database consists of a number of interrelated tables.

 Each table has a number of records which are used to represent real world objects. –

  • For example, the police may have a record for each criminal that has ever been arrested (i.e., the “rap”-sheet)

Each record has a number of fields which are data items used to specify a characteristic of the record.

Examples of fields are:

– name – employee number – address – prior convictions etc… 

What is RDMS?

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 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 employee table − 

+-----+--------+------------+--------+

| Id  | name   | dept      | salary |

+-----+--------+------------+--------+

| 100 | Thomas| Sales      |   5000 |

| 200 | Jason | Technology |   5500 |

| 300 | Mayla | Technology |   7000 |

| 400 | Nisha | Marketing  |   9500 |

| 500 | Randy | Technology |   6000 |

+-----+--------+------------+--------+

 5 rows in set (0.00 sec)

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 5 records in the above EMPLOYEE  table. Following is a single row of data or record in the EMPLOYEE  table −

+-----+--------+------------+--------+

| id  | name   | dept       | salary |

+-----+--------+------------+--------+

| 100 | Thomas | Sales      |   5000 |

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 EMPLOYEE table is DEPT, which represents location description and would be as shown below –

-+------------+

 | dept       |

-+------------+

 | Sales      |

 | Technology |

 | Technology |

 | Marketing  |

 | Technology |

-+------------+

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.

Difference between RDBMS AND DBMS

BASIS FOR COMPARISON

DBMS

RDBMS

 

Stands for

Database Management System

Relational Database Management System

 

Data storage

Data is stored in the navigational model.

Data is stored in the relational model (in tables).

 

Data redundancy

Exhibit

Does not present

 

Normalization

Not performed

RDBMS uses normalization to reduce or eliminate redundancy.

 

Modifiability

Modification in data is complex.

Modification in data is easy and simple.

 
 

Data access

Consumes more time.

Faster as compared to DBMS.

 

Schema-based constraints and data dependencies

Not employed

Employed in RDBMS.

 

Keys and indexes

Does not used.

To establish relationship keys and indexes are used in RDBMS.

 

Transaction management

Inefficient, error prone and insecure.

Efficient and secure.

 

Distributed Databases

Not supported

Supported by RDBMS.

 

Example

Dbase, Microsoft Access, LibreOffice Base, FoxPro.

SQL server, Oracle, mysql, MariaDB, SQLite.

 

 

SQL Databases

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 23rdMay 1995.
  • Windows Version was released on the 8thJanuary 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 26thFebruary 2008.
  • Version 5.1: production release 27thNovember 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.