SQL Basics Overview: What SQL Is and How It Works

SQL (Structured Query Language) is the language we use to work with data stored in a database. It allows us to create tables, insert new information, update existing records, and retrieve the exact data we need. Most SQL commands fall into a few groups:

DDL defines the structure of the database (like creating or modifying tables).
DML handles everyday operations such as adding, changing, or removing data.
DQL is mainly the SELECT command used to read data.
DCL controls access and permissions.
TCL manages transactions using COMMIT, ROLLBACK, and related commands.

In simple words, SQL gives us a systematic way to store data, organize it, and make it useful. These basics form the foundation of working with any relational DBMS.

Want to learn all SQL commands with examples?

Visit our article – SQL Basic Explained: Commands, Queries , and Examples.

DDL Commands — Overview

DDL (Data Definition Language) commands are used to define and manage the structure of a database. With DDL, we can create new tables, change the design of existing tables, or remove database objects that are no longer needed. Common DDL commands include:

CREATE – to create tables, databases, or other objects
ALTER – to modify an existing table (add, remove, or change columns)
DROP – to delete a table or database permanently
TRUNCATE – to remove all rows from a table quickly
RENAME – to change the name of a table

In short, DDL commands help set up the database structure so that data can be stored and used correctly.

DML Commands — Overview

DML (Data Manipulation Language) commands are used to work with the actual data stored in a table. These commands let us add new records, modify existing information, or remove data that is no longer required. The most common DML commands are:

INSERT – to add new rows of data
UPDATE – to change values in existing rows
DELETE – to remove specific rows from a table

In short, DML helps us manage day-to-day data operations inside the database. These commands do not change the structure of tables; they only work with the data stored in them.

DQL — Overview

DQL (Data Query Language) is mainly focused on retrieving information from the database. It helps us select specific rows, apply conditions, sort results, and combine data from multiple tables.
The primary DQL command is:

SELECT – used to read data from one or more tables

In simple terms, DQL allows users to ask questions from the database and get meaningful, organised results.

DCL — Overview

DCL (Data Control Language) commands are used to control access to the database. They help the administrator decide who can view, modify, or manage the data.
Common DCL commands include:

GRANT – to give permissions to a user
REVOKE – to remove previously given permissions

In short, DCL ensures that data is accessed only by authorized users and follows security rules set by the organization.

TCL — Overview

TCL (Transaction Control Language) commands are used to manage transactions in a database. These commands ensure that a group of operations is completed safely and consistently. If everything goes well, the changes are saved; if something goes wrong, the database can roll back to a previous stable state.
Common TCL commands include:

COMMIT – permanently saves all changes made in the transaction
ROLLBACK – cancels the transaction and restores the previous state
SAVEPOINT – creates a checkpoint inside a transaction that you can roll back to

In simple terms, TCL helps maintain data reliability by controlling how and when changes are applied during a transaction.

Want to learn more about transaction management?

Visit our article – Transaction Processing in DBMS: Concepts, Properties, and Examples.

DDL Commands — Overview

DML Commands — Overview

DQL — Overview

DCL — Overview

TCL — Overview

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