One post tagged with "Unique"

In PostgreSQL, a unique constraint ensures that the values in one or more columns of a table are unique across all rows. This means that no two rows in the table can have the same value(s) for the specified column(s). It's a common feature used to enforce data integrity and ensure that duplicate data cannot be stored.

How It Works​

• A unique constraint creates an implicit index on the column(s) it is applied to. This index is used to enforce the uniqueness of the values.
• A unique constraint can be defined on a single column or a combination of multiple columns.

Key Characteristics​

1. Single-Column Uniqueness: Ensures that no two rows have the same value in a single column.

   CREATE TABLE users (
       id SERIAL PRIMARY KEY,
       email VARCHAR(255) UNIQUE
   );
   
   In this example:
   • The email column must have unique values.