SQL Basics, DDL, DML, DCL, TCL, and Everyday Queries
Learn the language used to define, query, modify, secure, and manage relational databases in real projects.
Inside this chapter
- What SQL Is
- Important SQL Categories
- Basic Table and Insert Example
- Basic Query Example
- Update and Delete Carefully
- Real Usage Example
Series navigation
Study the chapters in order for the clearest path from database fundamentals and SQL to transactions, indexing, recovery, distributed systems, tuning, and advanced DBMS engineering understanding. Use the navigation at the bottom to move smoothly across the full tutorial series.
What SQL Is
SQL, or Structured Query Language, is the standard language used to communicate with relational databases. SQL is used for creating tables, retrieving data, updating records, controlling permissions, and managing transactions.
Important SQL Categories
- DDL: Data Definition Language such as CREATE, ALTER, DROP
- DML: Data Manipulation Language such as INSERT, UPDATE, DELETE
- DQL: Data Query Language, typically SELECT
- DCL: Data Control Language such as GRANT, REVOKE
- TCL: Transaction Control Language such as COMMIT, ROLLBACK
Basic Table and Insert Example
CREATE TABLE Students (
student_id INT PRIMARY KEY,
name VARCHAR(100),
email VARCHAR(150) UNIQUE
);
INSERT INTO Students (student_id, name, email)
VALUES (1, 'Asha', 'asha@example.com');Basic Query Example
SELECT student_id, name
FROM Students
WHERE name LIKE 'A%';Students should practice filtering, sorting, projection, and conditions because these are the building blocks of database interaction in applications and reporting tools.
Update and Delete Carefully
UPDATE Students
SET email = 'asha.p@example.com'
WHERE student_id = 1;
DELETE FROM Students
WHERE student_id = 1;In production systems, a missing WHERE clause can cause major damage. This is why safe habits and transaction awareness matter.
Real Usage Example
An HR system may use SQL to add employees, update department assignments, search by role, revoke access, and generate management reports. SQL is therefore both a developer tool and a business reporting tool.