Introduction To SQL And SQL Commands

 

In this chapter, we will learn about SQL and SQL Commands.

 

 

SQL stands for Structured Query Language. SQL is used to create, remove, alter the database and database objects in a database management system and to store, retrieve, update the data in a database. SQL is a standard language for creating, accessing, manipulating database management system. SQL works for all modern relational database management systems, like SQL Server, Oracle, MySQL, etc.

 

 

SQL commands can be categorized into five categories based on their functionality.

 

 

DDL stands for data definition language. DDL commands are used for creating and altering the database and database object in the relational database management system, like CREATE DATABASE, CREATE TABLE, ALTER TABLE, etc. The most used DDL commands are CREATE, DROP, ALTER, and TRUNCATE.

• CREATE
   
  CREATE command is used to create a database and database object like a table, index, view, trigger, stored procedure, etc.
   
  Syntax

  CREATE TABLE Employee (Id INT, Name VARHCAR(50), Address VARCHAR (100));
   
• ALTER
   
  ALTER command is used to restructure the database object and the settings in the database.
   
  Syntax
  ALTER TABLE Employee ADD Salary INT;
   
• TRUNCATE
   
  The TRUNCATE command is used to remove all the data from the table. TRUNCATE command empties a table.
   
  Syntax
  TRUNCATE TABLE Employee;
   
• DROP
   
  DROP command is used to remove the database and database object.
   
  Syntax
  DROP TABLE Employee;

 

DML stands for Data Manipulation Language. DML commands are used for manipulating data in a relational database management system. DML commands are used for adding, removing, updating data in the database system, like INSERT INTO TableName, DELETE FROM TableName, UPDATE tableName set data, etc. The most used DML commands are INSERT INTO, DELETE FROM, UPDATE.

• INSERT INTO
   
  INSERT INTO command is used to add data to the database table.
   
  Syntax
  INSERT INTO Employee (Id, Name, Address, Salary) VALUES (1, ‘Arvind Singh’, ‘Pune’, 1000);
   
• UPDATE
   
  UPDATE command is used to update data in the database table. A condition can be added using the WHERE clause to update a specific row.
   
  Syntax
  UPDATE Employee SET Address = ‘Pune India’, Salary = 100 WHERE Id =1;
   
• DELETE
   
  DELETE command is used to remove data from the database table. A condition can be added using the WHERE clause to remove a specific row that meets the condition.
   
  Syntax
  DELETE FROM Employee WHERE Id =1;

DQL

 

DQL stands for the Data Query Language. DQL command is used for fetching the data. DQL command is used for selecting data from the table, view, temp table, table variable, etc. There is only one command under DQL which is the SELECT command.

 

 

 

DCL stands for Data Control Language. DCL commands are used for providing and taking back the access rights on the database and database objects. DCL command used for controlling user’s access to the data. Most used DCL commands are GRANT and REVOKE.

 

TCL stands for transaction control language. TCL commands are used for handling transactions in the database. Transactions ensure data integrity in the multi-user environment. TCL commands can rollback and commit data modification in the database. The most used TCL commands are COMMIT, ROLLBACK, SAVEPOINT, and SET TRANSACTION.

 

 

Summary

 

In this chapter, we discussed SQL commands and their fundamentals.