The query below lists all primary keys constraints (PK) in the database.
See also: tables with their primary keys.
select schema_name(tab.schema_id) as [schema_name], pk.[name] as pk_name, substring(column_names, 1, len(column_names)-1) as [columns], tab.[name] as table_name from sys.tables as tab inner join sys.indexes as pk on tab.object_id = pk.object_id and pk.is_primary_key = 1 cross apply (select col.[name] + ', ' from sys.index_columns as ic inner join sys.columns as col on ic.object_id = col.object_id and ic.column_id = col.column_id where ic.object_id = tab.object_id and ic.index_id = pk.index_id order by col.column_id for xml path ('') ) D (column_names) order by schema_name(tab.schema_id), pk.[name]