SQL(Structured Query Language)

Introduction to SQL

SQL is the standard language for making queries in relational database management packages such as SQL Server, Ingress, Sybase, Oracle, etc. The standard language for accessing client/server database is also SQL. It is pronounced as SEQUEL or Structured Query Language. This forth generation language is very powerful and simple to use because it uses compact English like statements and performs very complex jobs to access information from a large sized database which was initially developed by IBM and modified by various other software designers. Although SQL language was first commercially implemented by Oracle Corporation in the year 1979 but there was no official standard until 1986. Hence when a non-programmer sits on a computer and wants to work with a database, he or she would like to use a simple high level language which can enable him/her to utilize databases available on a computer completely and easily for that purpose developers have developed SQL and modified it time by time.

History

Although SQL language was first commercially implemented by Oracle Corporation in the year 1979, there was no official standard until 1986. In 1986, SQL was jointly published by ANSI(American National Standards Institute) and the ISO(International Standards Organization). The SQL86 standard was revised in 1989 to introduce features that enforce referential integrity. By the time 86 standard appeared, a number of products in the market already used SQL, and the ISO attempted to draft a standard to which they could all conform relatively painlessly. Also, with the world becoming interconnected and heterogeneous computing becoming popular, developers and users wanted to be able to interface the various database engines. As a result there arose a demand for standardization of SQL features. To address these needs, ISO developed SQL 92 standard. SQL 92 is over five times the length of the first standard. In SQ 92, data is organized in a much better way. Data is contained in tables, tables are grouped into schemas and schemas are grouped into catalogs. The catalogs can be further grouped into clusters. 

 A. Schema definition statements.  

B. Temporary tables. 

C. Built-in join operators. 

D. Read-only, scrollable and dynamic cursors.

E. Standardized connection procedure.

F. Standardized error codes and diagnostics.

G. Altering and dropping objects.

Characteristics

Characteristics of SQL

1. SQL is oriented specifically around relational databases.

2. SQL commands  can operate on several groups of tables as single object. Also it processes any quantity of information, retrieved from these tables, as a single unit. 

3. SQL allows use of temporary tables. Temporary tables are used for storing intermediate results. They are useful only for the duration the program is in execution, and gets deleted when the program is terminated.

4. SQL is well suited to a client server environment, where the DBMS resides of a server and services the client requests. Features such as connection management, locking schemas and error diagnostics enable clients to communicate with a variety of DBMS packages.

5. SQL provides a flexible transaction management. A transaction is a group of SQL statements that succeed or fail as a group. That is, if any one of the SQL statements fail, the whole transaction is aborted.

6. SQL allows users to create domains as objects in a schema. The users can then declare table columns to be of domains rather than that of data types.

7. SQL allows one to specify constraints. Constraints are rules for restricting the values that can be placed in a table column. 

8. Privileges can be granted or denied using SQL commands. Privileges are the rights to perform actions on database objects.

Advantages

SQL has several simple to use commands for data processing activities. 

You can use SQL commands for the following purposes :-

 A. Creating(Defining) deleting, and modifying table structure.

B. Defining the relationship between two or more tables.

C. Inserting data into tables.

D. Extracting data in meaningful ways, based on the table’s defined relationship.

E. Updating data. This includes maintaining data in a database, and manipulating the stored values to keep the information current. 

F. Controlling a database. This includes system security and authorization which must be controlled and maintained. 

Installation

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Types of SQL

There are two types of SQL

A. Interactive SQL.    B. Embedded SQL. 

Interactive SQL  

Interactive SQL is used to operate directly on a database to produce output for desired purpose. In this form of SQL, a command is entered and executed. The output can be seen immediately.

Embedded SQL 

Embedded SQL consists of SQL commands put inside the program which are written in other high level language (such as COBOL, Pascal, C or C++). This method makes query system more powerful and efficient. However, enabling these languages to deal with SQL’s structure and its style of data management does require some extensions to interactive SQL. The output of SQL commands in embedded SQL is “passed off” to variables or parameters which are used by the program in which SQL commands are embedded. “Interactive SQL is the from most useful for non-programmers. When you learn commands about interactive SQL, the same commands also apply to embedded SQL