What is SQL?

SQL is a database language designed for the retrieval and management of data in a relational database.

SQL is the standard language for database management. All the RDBMS systems like MySQL, MS Access, Oracle, Sybase, Postgres, and SQL Server use SQL as their standard database language.

In this DBMS tutorial, you will learn:

Why Use SQL?

Here, are important reasons for using SQL

  • It helps users to access data in the RDBMS system.
  • It helps you to describe the data.
  • It allows you to define the data in a database and manipulate that specific data.
  • With the help of SQL, you can create and drop databases and tables.
  • SQL offers you to use the function in a database, create a view, and stored procedure.
  • You can set permissions on tables, procedures, and views.

Brief History of SQL

Here, are important landmarks from the history of SQL:

  • 1970 - Dr. Edgar F. "Ted" Codd described a relational model for databases.
  • 1974 - Structured Query Language appeared.
  • 1978 - IBM released a product called System/R.
  • 1986 - IBM developed the prototype of a relational database, which is standardized by ANSI.
  • 1989- First ever version launched of SQL
  • 1999 - SQL 3 launched with features like triggers, object-orientation, etc.
  • SQL2003- window functions, XML-related features, etc.
  • SQL2006- Support for XML Query Language
  • SQL2011-improved support for temporal databases

Types of SQL

Here are five types of widely used SQL queries.

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

Let see each of them in detail:

What is DDL?

Data Definition Language helps you to define the database structure or schema.

Five types of DDL commands are:

CREATE

CREATE statements is used to define the database structure schema:

Syntax:

CREATE TABLE TABLE_NAME (COLUMN_NAME DATATYPES[,....]); 

For example:

Create database university;
Create table students;
Create view for_students;

DROP

Drops commands remove tables and databases from RDBMS.

Syntax

DROP TABLE ;

For example:

Drop object_type object_name;
Drop database university;
Drop table student;

ALTER

Alters command allows you to alter the structure of the database.

Syntax:

To add a new column in the table

ALTER TABLE table_name ADD column_name COLUMN-definition; 

To modify an existing column in the table:

ALTER TABLE MODIFY(COLUMN DEFINITION....);  

For example:

Alter table guru99 add subject varchar; 

TRUNCATE:

This command used to delete all the rows from the table and free the space containing the table.

Syntax:

TRUNCATE TABLE table_name;  

Example:

TRUNCATE table students;

What is Data Manipulation Language?

Data Manipulation Language (DML) allows you to modify the database instance by inserting, modifying, and deleting its data. It is responsible for performing all types of data modification in a database.

There are three basic constructs which allow database program and user to enter data and information are:

Here are some important DML commands:

  • INSERT
  • UPDATE
  • DELETE

INSERT:

This is a statement is a SQL query. This command is used to insert data into the row of a table.

Syntax:

INSERT INTO TABLE_NAME  (col1, col2, col3,.... col N)  
VALUES (value1, value2, value3, .... valueN);  
Or 
INSERT INTO TABLE_NAME    
VALUES (value1, value2, value3, .... valueN);    

For example:

INSERT INTO students (RollNo, FIrstName, LastName) VALUES ('60', 'Tom', Erichsen');

UPDATE:

This command is used to update or modify the value of a column in the table.

Syntax:

UPDATE table_name SET [column_name1= value1,...column_nameN = valueN] [WHERE CONDITION]   

For example:

UPDATE students    
SET FirstName = 'Jhon', LastName= 'Wick' 
WHERE StudID = 3;

DELETE:

This command is used to remove one or more rows from a table.

Syntax:

DELETE FROM table_name [WHERE condition];  

For example:

DELETE FROM students 
WHERE FirstName = 'Jhon';

What is DCL?

DCL (Data Control Language) includes commands like GRANT and REVOKE, which are useful to give "rights & permissions." Other permission controls parameters of the database system.

Examples of DCL commands:

Commands that come under DCL:

  • Grant
  • Revoke

Grant:

This command is use to give user access privileges to a database.

Syntax:

GRANT SELECT, UPDATE ON MY_TABLE TO SOME_USER, ANOTHER_USER;  

For example:

GRANT SELECT ON Users TO'Tom'@'localhost;

Revoke:

It is useful to back permissions from the user.

Syntax:

REVOKE privilege_nameON object_nameFROM {user_name |PUBLIC |role_name}

For example:

REVOKE SELECT, UPDATE ON student FROM BCA, MCA;  

What is TCL?

Transaction control language or TCL commands deal with the transaction within the database.

Commit

This command is used to save all the transactions to the database.

Syntax:

Commit;

For example:

DELETE FROM Students  
WHERE RollNo =25;  
COMMIT;  

Rollback

Rollback command allows you to undo transactions that have not already been saved to the database.

Syntax:

ROLLBACK;  

Example:

DELETE FROM Students  
WHERE RollNo =25;  

SAVEPOINT

This command helps you to sets a savepoint within a transaction.

Syntax:

SAVEPOINT SAVEPOINT_NAME;

Example:

SAVEPOINT RollNo;

What is DQL?

Data Query Language (DQL) is used to fetch the data from the database. It uses only one command:

SELECT:

This command helps you to select the attribute based on the condition described by the WHERE clause.

Syntax:

SELECT expressions    
FROM TABLES    
WHERE conditions;  

For example:

SELECT FirstName  
FROM Student  
WHERE RollNo > 15;  

Summary:

  • SQL is a database language designed for the retrieval and management of data in a relational database.
  • It helps users to access data in the RDBMS system
  • In the year 1974, the term Structured Query Language appeared
  • Five types of SQL queries are 1) Data Definition Language (DDL) 2) Data Manipulation Language (DML) 3) Data Control Language(DCL) 4) Transaction Control Language(TCL) and, 5) Data Query Language (DQL)
  • Data Definition Language(DDL) helps you to define the database structure or schema.
  • Data Manipulation Language (DML) allows you to modify the database instance by inserting, modifying, and deleting its data.
  • DCL (Data Control Language) includes commands like GRANT and REVOKE, which are useful to give "rights & permissions."
  • Transaction control language or TCL commands deal with the transaction within the database.
  • Data Query Language (DQL) is used to fetch the data from the database.

 

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