if object_id('[tb]') is not null drop table [tb]
go
create table [tb]([id] int,[name] varchar(2),[tel] varchar(3),[departTime] datetime)
insert [tb]
select 1,'11','22','2012-07-17 00:00:00' union all
select 8,'ab','c','2012-07-17 00:00:00' union all
select 9,'ab','123','2012-07-17 00:00:00' union all
select 10,'ab','123','2012-07-18 00:00:00' union all
select 11,'ab','123','2012-06-13 00:00:00'
go

select name,tel,avg(dt) as [avg]
from
(
select *,
datediff(dd,departtime,isnull((select top 1 departtime from tb where name=t.name and tel=t.tel and departtime>t.departtime order by departtime),departtime)) as dt
from tb t
) t
group by name,tel

/**
name tel  avg
---- ---- -----------
ab   123  11
11   22   0
ab   c    0

(3 行受影响)
**/

------解决方案--------------------
SQL code
CREATE TABLE #TEMP(ID INT,NAME VARCHAR(30),TEL VARCHAR(30), DEPARTTIME DATETIME)
GO
INSERT INTO #TEMP
SELECT 1, '11', '22', '2012-07-17 00:00:00' UNION ALL
SELECT 8 ,'AB', 'C' ,'2012-07-17 00:00:00' UNION ALL
SELECT 9, 'AB', '123' ,'2012-07-17 00:00:00' UNION ALL
SELECT 10, 'AB', '123', '2012-07-18 00:00:00' UNION ALL
SELECT 11, 'AB', '123', '2012-06-13 00:00:00' 
GO

SELECT NAME,TEL,AVG(DT) AS [AVG]
FROM
(
SELECT ID,NAME,TEL,
DATEDIFF(DD,DEPARTTIME,ISNULL((SELECT TOP 1 DEPARTTIME FROM #TEMP WHERE NAME=T.NAME AND TEL=T.TEL AND ID != T.ID AND DEPARTTIME>=T.DEPARTTIME ORDER BY DEPARTTIME),DEPARTTIME)) DT
FROM #TEMP T
) T
GROUP BY NAME,TEL
ORDER BY MIN(ID)




DROP TABLE #TEMP
GO

-----------------------
11    22    0
AB    C    0
AB    123    11

------解决方案--------------------

SQL code

--> 测试数据：[A1]
if object_id('[A1]') is not null 
drop table [A1]
create table [A1](
[id] int,
[name] varchar(2),
[tel] varchar(3),
[departTime] datetime
)
go
insert [A1]
select 1,'11','22','2012-07-17 00:00:00' union all
select 8,'ab','c','2012-07-17 00:00:00' union all
select 9,'ab','123','2012-07-17 00:00:00' union all
select 10,'ab','123','2012-07-18 00:00:00' union all
select 11,'ab','123','2012-06-13 00:00:00'
go

;with t
as(
select 
    px=ROW_NUMBER()over(partition by [name],[tel] order by [departTime] asc),
    *
from
    [A1]
),
m as
(
select 
    px,
    name,
    tel,
    [departTime],
    0 as TotalDays
from 
    t
where 
    px=1
union all
select 
    a.px,
    a.name,
    a.tel,
    a.[departTime],
    DATEDIFF(dd,m.[departTime],a.departTime)
from 
    t a
inner join 
    m
on 
    a.px=m.px+1 and a.tel=m.tel
)
--select * from m
select 
    name,
    tel,
    AVG(TotalDays) as TotalDays 
from 
    m 
group by
    name,tel
/*
name    tel    TotalDays
-----------------------------------
ab    123    11
11    22    0
ab    c    0
*/