What is the primary key rule in PostgreSQL?

What is the primary key rule?

Rules for Primary Key The rules of Primary Key are as follows: All the values in the column chosen as the primary key must be unique. Each and every table can have only one primary key. No value in the primary key column can be NULL. You cannot insert a new row with a pre-existing primary key.

What is primary key in Postgres?

What is a primary key in PostgreSQL? In PostgreSQL, a primary key is a single field or combination of fields that uniquely defines a record. None of the fields that are part of the primary key can contain a NULL value. A table can have only one primary key.

What are the two rules of primary key?

The general rules when designing a primary key are:The primary key value must uniquely identify one and only one record within the table. ... The primary key value must NOT be null. ... The primary key value must NOT change.

Is primary key mandatory in PostgreSQL?

A table with no primary key will only send out INSERTs on the logical decoding stream; UPDATEs and DELETEs are lost. Reading the postgres docs at postgresql.org/docs/10/static/…