Lesson 28: Change Data Types & Add Constraints in PostgreSQL ALTER TABLE Guide
In this lesson, you will learn how to use the ALTER TABLE command in PostgreSQL to modify existing columns by changing their data types and adding constraints.
You will see how to update a column’s data type (for example, from INTEGER to VARCHAR) and how to apply rules like NOT NULL, UNIQUE, CHECK, or DEFAULT to control and protect your data. These changes help improve data accuracy and enforce proper data entry.
By the end of this lesson, you will understand how to safely modify table structure and apply important rules to existing columns in a simple, step-by-step way.