Explain the difference between the PRIMARY KEY and UNIQUE constraints in PostgreSQL.

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Answered by suresh

Primary Key vs Unique Constraint in PostgreSQL

Primary Key vs Unique Constraint in PostgreSQL

The primary key and unique constraint are important concepts in PostgreSQL that help ensure data integrity and uniqueness in tables.

Primary Key

The PRIMARY KEY constraint in PostgreSQL is used to uniquely identify each record in a table. It ensures that each value in the specified column(s) is unique and not null. By default, a primary key also creates a unique index on the column(s) to enforce uniqueness and faster data retrieval.

Unique Constraint

The UNIQUE constraint in PostgreSQL also ensures the uniqueness of values within a column or a group of columns. However, unlike the primary key, a table can have multiple unique constraints, and the unique constraint does not automatically create a corresponding index.

Focus Keyword: PostgreSQL PRIMARY KEY vs UNIQUE Constraint

In summary, the primary key is used to uniquely identify each record in a table and automatically creates a unique index, while the unique constraint ensures uniqueness but does not necessarily create an index.

Answer for Question: Explain the difference between the PRIMARY KEY and UNIQUE constraints in PostgreSQL.