Introduction to SQL : SQL stands for Structured Query Language or we can call it as "sequel" or "S-Q-L" . SQL is a query Language used to accessing and modifying information in a database.There are some common SQL command used which are "Select", "Insert", "Update" and "Delete". SQL was first created by IBM in 1975 and it was called "Structured English Query Language", Today SQL is mostly used for Website database development and management. We can execute SQL commands by using PHP scripting language when a web page loads. With this, we can display a different information each time the page loads. There are four types of SQL command used in database programming.

SQL commands are categorized below :-

• DDL (Data Definition Language)
• DML (Data Manipulation Language)
• DCL (Data Control Language)
• TCL (Transaction Control Language)

• DDL (Data Definition Language) :

  DDL is knows as Data Definition Language, these are the commands used to define the structure of database objects. SQL commands used for data definition language are CREATE, ALTER, DROP, TRUNCATE and RENAME.

  
  
• DML (Data Manipulation Language) :

  DML known as Data Manipulation Language, these are the commands used to manage data within database tables. SQL commands used for data manipulation are SELECT, INSERT, UPDATE and DELETE.

  
  
• DCL (Data Control Language) :

  DCL known as Data Control Language, It is used to set control to access data from the database. In Data Control Language, commands are mainly used for creating roles, set permissions and privileges for access to database. SQL commands used for data control are GRANT and REVOKE.

  
  
• TCL (Transaction Control Language) :

  TCL known as Transaction Control Language, these are the commands used to manage the transactions which cause the changes in data which is stored in database. SQL commands used for transaction control are COMMIT, ROLLBACK, SAVEPOINT and SET TRANSACTION

  
  

We are going to learn all the above commands in detail in next chapters.