Do you feel lost when it comes to SQL commands? If yes, don’t worry! SQL might seem intimidating at first, but once you understand the types of commands, you’ll be writing queries like a pro in no time.
By the end of this post, you’ll feel more confident using SQL and know exactly which command to use in various situations.
What are the Different Types of SQL Commands
There are types of SQL commands and each command have different purpose to serve which we will discuss in this article.
But first let us understand What Are SQL Commands to be exact .
What Are SQL Commands?
SQL is a language we use to interact with databases and to interact with we need SQL commands.
Consider SQL commands as instructions you give to a database to either fetch, modify, or manage your data.
Why Understanding SQL Commands is Important
Knowing the different types of SQL commands helps in database management, ensuring efficient data handling and security. With a good grasp of these commands, you’ll be able to:
- Create and modify database structures.
- Insert, update, and delete data.
- Retrieve data from the database.
- Control access and permissions.
- Manage transactions to ensure data integrity.
By mastering these commands, you’ll feel more confident in your data journey. SQL is the most important skill for Data Analyst or any data domain job.
Related – How to learn SQL for Data Analysis – SQL Roadmap
All SQL commands fall into different categories, each is used for different purpose. Let’s dive into these categories and break them down with examples. DQL command. It allows you to specify which columns you want to retrieve and from which tables.
Why Understanding SQL Commands is Important
Knowing the different types of SQL commands helps in database management, ensuring efficient data handling and security. With a good grasp of these commands, you’ll be able to:
- Create and modify database structures
- Insert, update, and delete data
- Retrieve data from the database
- Control access and permissions
- Manage transactions to ensure data integrity
By mastering these commands, you’ll feel more confident in handling databases, whether you’re a beginner or an experienced professional.
Types of SQL Commands
There are five major categories of SQL commands, each serving a unique purpose. Let’s explore them in detail.
1. Data Definition Language (DDL)
Purpose: DDL commands define the structure of the database. You use these commands to create, alter, or delete database objects like tables, indexes, and schemas.
Common DDL Commands:
- CREATE: Used to create new objects such as tables or databases.
Syntax:CREATE TABLE table_name (column1 data_type, column2 data_type); - ALTER: Modifies the structure of an existing table.
Syntax:ALTER TABLE table_name ADD column_name data_type; - DROP: Deletes objects like tables or databases from the system.
Syntax:DROP TABLE table_name; - TRUNCATE: Removes all rows from a table, but keeps the structure.
Syntax:TRUNCATE TABLE table_name;
DDL (Data Definition Language) Commands
| Command | Description | Syntax |
|---|---|---|
| CREATE | Create database or its objects (table, index, function, views, etc.) | CREATE TABLE table_name (column1 data_type, column2 data_type, ...); |
| DROP | Delete objects from the database | DROP TABLE table_name; |
| ALTER | Modify the structure of the database | ALTER TABLE table_name ADD COLUMN column_name data_type; |
| TRUNCATE | Remove all records from a table, but retain the structure | TRUNCATE TABLE table_name; |
| COMMENT | Add comments to the data dictionary | COMMENT 'comment_text' ON TABLE table_name; |
| RENAME | Rename an object in the database | RENAME TABLE old_table_name TO new_table_name; |
2. Data Manipulation Language (DML)
Purpose: DML commands manipulate the data within the database. This includes inserting new data, updating existing data, or deleting data.
Common DML Commands:
- INSERT: Adds new rows to a table.
Syntax:INSERT INTO table_name (column1, column2) VALUES (value1, value2); - UPDATE: Modifies existing data in a table.
Syntax:UPDATE table_name SET column1 = value1 WHERE condition; - DELETE: Removes rows from a table.
Syntax:DELETE FROM table_name WHERE condition;
DML (Data Manipulation Language) Commands
| Command | Description | Syntax |
|---|---|---|
| INSERT | Insert data into a table | INSERT INTO table_name (column1, column2, ...) VALUES (value1, value2, ...); |
| UPDATE | Update existing data within a table | UPDATE table_name SET column1 = value1 WHERE condition; |
| DELETE | Delete records from a table | DELETE FROM table_name WHERE condition; |
| MERGE | Combine two tables based on conditions | MERGE INTO target_table USING source_table ON condition WHEN MATCHED THEN action; |
3. Data Query Language (DQL)
Purpose: DQL is used for querying data from the database. The primary command here is SELECT, which is used to retrieve specific data based on given conditions.
DQL Command:
- SELECT: Retrieves data from one or more tables.
Syntax:SELECT column1, column2 FROM table_name WHERE condition;
DQL (Data Query Language) Commands
| Command | Description | Syntax |
|---|---|---|
| SELECT | Retrieve data from the database | SELECT column1, column2 FROM table_name WHERE condition; |
4. Data Control Language (DCL)
Purpose: DCL commands manage permissions and access controls. These commands ensure that the right users have access to the right data.
Common DCL Commands:
- GRANT: Gives specific permissions to a user.
Syntax:GRANT privilege_type ON object_name TO user; - REVOKE: Removes previously granted permissions from a user.
Syntax:REVOKE privilege_type ON object_name FROM user;
DCL (Data Control Language) Commands
| Command | Description | Syntax |
|---|---|---|
| GRANT | Provide user access privileges | GRANT privilege_name ON object TO user; |
| REVOKE | Remove user access privileges | REVOKE privilege_name ON object FROM user; |
5. Transaction Control Language (TCL)
Purpose: TCL commands manage transactions in the database, which are sequences of SQL commands treated as a single unit. These commands ensure the consistency of data.
Common TCL Commands:
- COMMIT: Saves the changes made during a transaction.
Syntax:COMMIT; - ROLLBACK: Reverts the changes made during a transaction in case of errors.
Syntax:ROLLBACK; - SAVEPOINT: Creates a savepoint within a transaction, allowing partial rollbacks.
Syntax:SAVEPOINT savepoint_name;
TCL (Transaction Control Language) Commands
| Command | Description | Syntax |
|---|---|---|
| COMMIT | Save all the transactions in the database | COMMIT; |
| ROLLBACK | Undo changes made to the database in the current transaction | ROLLBACK; |
| SAVEPOINT | Set a savepoint within a transaction | SAVEPOINT savepoint_name; |
Summary of All Important SQL Commands with Examples
Below are some commonly used SQL commands with examples that you’ll frequently encounter in database management:
- SELECT: Retrieve all employees’ details.
SELECT * FROM employees; - INSERT: Add a new employee to the database.
INSERT INTO employees (first_name, last_name, email) VALUES ('John', 'Doe', 'john.doe@example.com'); - UPDATE: Update the email of an employee.
UPDATE employees SET email = 'jane.doe@example.com' WHERE first_name = 'Jane'; - DELETE: Remove an employee from the database.
DELETE FROM employees WHERE employee_id = 123; - CREATE TABLE: Create a new employee table.
CREATE TABLE employees (employee_id INT PRIMARY KEY, first_name VARCHAR(50)); - ALTER TABLE: Add a phone number column to the employee table.
ALTER TABLE employees ADD COLUMN phone VARCHAR(20); - DROP TABLE: Delete the employee table.
DROP TABLE employees;
Conclusion
SQL commands are essential for managing databases effectively.
Understanding the five categories—DDL, DML, DQL, DCL, and TCL—will equip you with the knowledge to perform any database-related task, from creating tables to managing transactions. With this guide, you’re now ready to handle SQL queries like a pro!
FAQ on SQL Commands
What are the 5 types of commands in SQL?
Data Definition Language (DDL): Used to create, modify, and delete database objects (tables, views, indexes).
Data Manipulation Language (DML): Used to insert, update, delete, and retrieve data from tables.
Data Control Language (DCL): Used to manage user privileges and permissions.
Transaction Control Language (TCL): Used to manage transactions and ensure data consistency
What is a SQL command?
A SQL command is a statement used to interact with a relational database. It provides instructions to the database management system (DBMS) to perform specific tasks, such as:
Retrieving data: Using the SELECT command to extract information from tables.
Modifying data: Using the INSERT, UPDATE, and DELETE commands to add, change, or remove data from tables.
Defining database structure: Using the CREATE, ALTER, and DROP commands to create, modify, and delete database objects like tables, views, and indexes.
Managing user privileges: Using the GRANT and REVOKE commands to control access to database objects.
Managing transactions: Using the COMMIT and ROLLBACK commands to control the execution of multiple database operations as a single unit.
