With below query we may find out the constraints of every table. It is useful in case when we want to update, delete any constraint.
USE Northwind;
GO
SELECT OBJECT_NAME(OBJECT_ID) AS NameofConstraint,
SCHEMA_NAME(schema_id) AS SchemaName,
OBJECT_NAME(parent_object_id) AS TableName,
type_desc AS ConstraintType
FROM sys.objects
WHERE type_desc LIKE '%CONSTRAINT'
Order by TableName
GO
Above query will list all tables with their constraints.