Reusing views to do aggregate queries
Following sample may be useful to build query which you want to write.

USE tempdb
GO

CREATE TABLE t_Ids (id VARCHAR(10) PRIMARY KEY )
GO

INSERT INTO t_Ids VALUES('id1'),('id2'),('id3'),('id4')
GO

CREATE VIEW v_V1
AS 
SELECT 'id1' id, 2 value UNION
SELECT 'id1' id, 1 UNION
SELECT 'id1' id, 3 UNION
SELECT 'id2' id, 1 
GO

CREATE VIEW v_V2
AS 
SELECT 'id3' id, 'London' city UNION
SELECT 'id3' id, 'Paris' UNION
SELECT 'id1' id, 'London' 
GO

SELECT t.id, ISNULL(SUM(v1.value), 0) AS agg_value,  COUNT(DISTINCT v2.city) cnt_city
FROM t_Ids AS t
LEFT OUTER JOIN v_v1 AS v1 ON t.id = v1.id
LEFT OUTER JOIN v_v2 AS v2 ON t.id = v2.id  
GROUP BY t.id
GO

DROP TABLE t_Ids
GO

DROP VIEW v_v1, v_v2
GO