For example, a unique constraint can be defined on the supplier identifier in the supplier table to ensure that the same supplier identifier is not given to two suppliers. A primary key constraint is a column or combination of columns that has the same properties as a unique constraint.
What are the three types of constraints?
The three primary constraints that project managers should be familiar with are time, scope, and cost. These are frequently known as the triple constraints or the project management triangle.
Is a unique constraint an index Postgres?
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.
How do I change unique index in PostgreSQL?
There is no way to change an index to unique index. You can see what you can change to index at alter index document. In this case you need to drop and create new unique index.12 sept 2017