What is unique about PostgreSQL?

What is Postgres unique index?

PostgreSQL automatically creates a unique index when a unique constraint or primary key is defined for a table. The index covers the columns that make up the primary key or unique constraint (a multicolumn index, if appropriate), and is the mechanism that enforces the constraint.

Is null unique in PostgreSQL?

Introduction to PostgreSQL UNIQUE index PostgreSQL treats NULL as distinct value, therefore, you can have multiple NULL values in a column with a UNIQUE index. When you define a primary key or a unique constraint for a table, PostgreSQL automatically creates a corresponding UNIQUE index.

What is primary key in PostgreSQL?

The PostgreSQL PRIMARY KEY is a column in a table which must contain a unique value which can be used to identify each and every row of a table uniquely. So it can be said that the PRIMARY KEY of a table is a combination of NOT NULL and UNIQUE constraint.

What is a unique index?

Unique indexes are indexes that help maintain data integrity by ensuring that no rows of data in a table have identical key values. When you create a unique index for an existing table with data, values in the columns or expressions that comprise the index key are checked for uniqueness.