MSSQL 取得下周行数据

SELECT *  FROM (
SELECT '2015-01-01' AS a
UNION 
SELECT '2015-01-02' AS a
UNION 
SELECT '2015-01-03' AS a
UNION 
SELECT '2015-01-04' AS a
UNION 
SELECT '2015-01-05' AS a
UNION 
SELECT '2015-01-06' AS a
UNION 
SELECT '2015-01-07' AS a
UNION 
SELECT '2015-01-08' AS a
UNION 
SELECT '2015-01-09' AS a
UNION 
SELECT '2015-01-10' AS a
UNION 
SELECT '2015-01-11' AS a
UNION 
SELECT '2015-01-12' AS a

) t 
 	WHERE  datediff(wk,t.a,getdate())=-1