If you work with an unknown schema and try to investigate the relationships between primary and foreign keys, there is a great answer on stackoverflow originally posted by db2.
SELECT
o1.name AS FK_table,
c1.name AS FK_column,
fk.name AS FK_name,
o2.name AS PK_table,
c2.name AS PK_column,
pk.name AS PK_name,
fk.delete_referential_action_desc AS Delete_Action,
fk.update_referential_action_desc AS Update_Action
FROM sys.objects o1
INNER JOIN sys.foreign_keys fk
ON o1.object_id = fk.parent_object_id
INNER JOIN sys.foreign_key_columns fkc
ON fk.object_id = fkc.constraint_object_id
INNER JOIN sys.columns c1
ON fkc.parent_object_id = c1.object_id
AND fkc.parent_column_id = c1.column_id
INNER JOIN sys.columns c2
ON fkc.referenced_object_id = c2.object_id
AND fkc.referenced_column_id = c2.column_id
INNER JOIN sys.objects o2
ON fk.referenced_object_id = o2.object_id
INNER JOIN sys.key_constraints pk
ON fk.referenced_object_id = pk.parent_object_id
AND fk.key_index_id = pk.unique_index_id
ORDER BY o1.name, o2.name, fkc.constraint_column_id