Understanding SQL Command Types/Categories: A Beginner’s Guide

Introduction

Structured Query Language (SQL) is a language used to work with database schemas. For those related in the IT industry, one could simply say taht It allows us to perform operations on existing databases and/or create new ones. Some examples of such SQL commands are CREATE, DROP, and INSERT and is mainly used to handle different set of tasks.

What are SQL Commands?

SQL commands are like instructions for a table. They help interact with databases to perform specific tasks, functions, and data queries. Some common tasks as also mentioned above that an SQL can perform includes creating tables, adding data, dropping tables, modifying tables, and setting user permissions. To know more about SQL Command Types/Categories, please refer to the details below:

Types/Categories of SQL Commands

DDL – Data Definition Language

DDL commands are used to define the structure of a database. These are employed to build and alter the composition of database objects like tables and indexes. Although it may differ from different roles in an organization, DDL commands are typically used by applications that access the database rather than by general users.

For instance, some DDL commands are:

• CREATE: Used to build tables, indexes, and view objects in databases.
• DROP: Used to delete objects from a database.
• ALTER: Used to change or modify the structure of a database.
• TRUNCATE: Used to eliminate all records from a table.
• COMMENT: Used to add comments to the data dictionary.
• RENAME: Used to rename an object in the database.

DQL – Data Query Language

Data from a database is retrieved using DQL statements. These enable users to organize the data and carry out operations on it. The SELECT command is the most widely used DQL command. From one or more tables, data is retrieved using this.

An example of a DQL command:

• SELECT: Used to retrieve data from the database.

DML – Data Manipulation Language

DML commands are used to manipulate data in the database. Here, users can use these to add, update, and delete records from tables.

Some examples of DML commands:

• INSERT: Used to insert data into a table.
• UPDATE: Used to update existing data in a table.
• DELETE: Used to delete records from a table.

DCL – Data Control Language

DCL commands are used to control the rights and permissions of the database system. These let users give or take away access privileges from other users.

Some examples of DCL commands:

• GRANT: Gives users access privileges to the database.
• REVOKE: Withdraws access privileges given by the GRANT command.

TCL – Transaction Control Language

TCL commands are used to control the execution of transactions. A group of tasks are combined into one work unit through transactions. These can be used to commit or roll back tasks, making them particularly useful when working with large amounts of data.

Some examples of TCL commands:

• BEGIN: Opens a transaction.
• COMMIT: Commits a transaction.
• ROLLBACK: Rolls back a transaction in case of an error.
• SAVEPOINT: Sets a save point within a transaction.