SQL Basics Explained: Commands, Data Types, and Constraints Demystified

SQL, or Structured Query Language, is the standard language used to manage and interact with data in relational database management systems. Its commands are grouped into five categories: DDL, DML, DQL, DCL, and TCL, each serving a distinct purpose from creating tables to controlling user access. When defining a table, each column must be assigned a data type — such as integer, text, or timestamp — to ensure only appropriate data is stored. Constraints like PRIMARY KEY, FOREIGN KEY, NOT NULL, and UNIQUE are applied alongside data types to enforce data integrity and prevent invalid entries. Together, these elements form the foundation of structured database design, enabling accurate, consistent, and efficient data management.