Guide to Databases Last Updated : 30 Aug, 2025 Comments Improve Suggest changes Like Article Like Report This is a complete guide to databases, where you’ll learn the foundations and advanced concepts of the most widely used database technologies -SQL: The standard language to interact with relational databases.MySQL: A popular open-source database used in web applications and enterprises.PostgreSQL: An advanced open-source relational database known for reliability and performance.PL/SQL: Oracle’s procedural extension of SQL for writing powerful database programs.MongoDB: A NoSQL database that stores data in flexible, JSON-like documents.Here, you’ll understand how each of these works, what they’re used for, and how they fit into real-world applications.1. SQLSQL TutorialSQL Interview QuestionsSQL Cheat SheetSQL Exercises 2. MySQLMySQL Tutorial MySQL Interview Questions3. PostgreSQLPostgreSQL TutorialPostgreSQL Cheat Sheet PostgreSQL Exercises4. PL/SQLPL/SQL TutorialPL/SQL Interview Questions and Answers5. MongoDBMongoDB TutorialComplete MongoDB RoadmapMongoDB Interview Questions with Answers MongoDB Exercises Comment U udaymityym1 Follow Improve U udaymityym1 Follow Improve Article Tags : SQL Explore SQL Tutorial 7 min read BasicsWhat is SQL? 6 min read SQL Data Types 3 min read SQL Operators 5 min read SQL Commands | DDL, DQL, DML, DCL and TCL Commands 4 min read SQL Database Operations 3 min read SQL CREATE TABLE 3 min read Queries & OperationsSQL SELECT Query 2 min read SQL INSERT INTO Statement 4 min read SQL UPDATE Statement 3 min read SQL DELETE Statement 3 min read SQL - WHERE Clause 3 min read SQL | Aliases 3 min read SQL Joins & FunctionsSQL Joins (Inner, Left, Right and Full Join) 4 min read SQL CROSS JOIN 2 min read SQL | Date Functions 4 min read SQL | String functions 6 min read Data Constraints & Aggregate FunctionsSQL NOT NULL Constraint 2 min read SQL PRIMARY KEY Constraint 5 min read SQL Count() Function 7 min read SQL SUM() Function 5 min read SQL MAX() Function 4 min read AVG() Function in SQL 4 min read Advanced SQL TopicsSQL Subquery 4 min read Window Functions in SQL 6 min read SQL Stored Procedures 7 min read SQL Triggers 5 min read SQL Performance Tuning 6 min read SQL TRANSACTIONS 6 min read Database Design & SecurityIntroduction of ER Model 10 min read Introduction to Database Normalization 6 min read SQL Injection 11 min read SQL Data Encryption 5 min read SQL Backup 4 min read What is Object-Relational Mapping (ORM) in DBMS? 7 min read Like