Introduction to SQL

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Introduction to SQL

What is SQL?

  • It stands for Structured Query Language.
  • It lets you access and manipulate databases.
  • 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 versions , such as −
    • MS SQL ( T-SQL),
    • Oracle (PL/SQL),
    • MS Access version of SQL is called JET SQL  likewise.

What Can SQL do?

  • It can execute queries against a database
  • It can retrieve data from a database
  • It can insert records in a database
  • It can update records in a database
  • It can delete records from a database
  • It can create new databases
  • It can create new tables in a database
  • It can create stored procedures in a database
  • It can create views in a database
  • It can set permissions on tables, procedures, and views

Why SQL?

It is widely popular because it offers the following advantages −

  • To access data in the relational database management systems.
  • To describe the data.
  • To define the data in a database and manipulate that data.
  • To embed within other languages using SQL-modules, libraries & pre-compilers.
  • To create and drop databases and tables.
  • To create view, stored procedure, functions in a database.
  • To set permissions on tables, procedures and views.

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
  • Optimisation 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.

RDBMS

RDBMS stands for Relational Database Management System.

RDBMS is the basis for SQL, and for all modern database systems such as MS-SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access.

The data in RDBMS is stored in database objects called tables. A table is a collection of related data entries and it consists of columns and rows.

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