Appear in the forum more difficult question sql: 29 (the value of a column in the function group row_number consecutive flagged 3 times)

Original: appearing in the forums more difficult question sql: 29 (the value of a column in the function group row_number consecutive flagged 3 times)

In the forum, I met a lot more difficult sql problem, although they can be resolved, but found a few days later, they can not remember, forget the solution of.

So, I feel the need to be recorded, so that after the encounter this problem again, and get answers from the idea.

A column value is set within 3 consecutive times marked

as follows, eid of personnel ID, for a same EID, date column appears more than 3 times, FLAG column labeled 1.
try to use an UPDATE statement!

eid date    flag
1 2013-3-1
1 2013-3-2
1 2013-3-4
1 2013-3-5
1 2013-3-7 1
1 2013-3-8 1
1 2013-3-9 1
1 2013-3-11
1 2013-3-12
1 2013-3-14 1
1 2013-3-15 1
1 2013-3-16 1
1 2013-3-18
2 2013-3-1
2 2013-3-2
2 2013-3-4
2 2013-3-6 1
2 2013-3-7 1
2 2013-3-8 1
2 2013-3-9 1
2 2013-3-11 1
2 2013-3-12 1
2 2013-3-13 1
2 2013-3-15
2 2013-3-16
2 2013-3-18 1
2 2013-3-19 1
2 2013-3-20 1
3 2013-3-1
3 2013-3-2
3 2013-3-4 1
3 2013-3-5 1
3 2013-3-6 1
3 2013-3-8
3 2013-3-9
3 2013-3-12 1
3 2013-3-13 1
3 2013-3-14 1
3 2013-3-15 1
3 2013-3-18 1
3 2013-3-19 1
3 2013-3-20 1

My method:

   
   
CREATE TABLE #t (eid INT, DATE DATETIME, flag INT )
GO

INSERT #t(eid, DATE,flag)
select 1, '2013-3-1', null union
select 1, '2013-3-2', null union
select 1, '2013-3-4', null union
select 1, '2013-3-5', null union
select 1, '2013-3-7', 1 union
select 1, '2013-3-8', 1 union
select 1, '2013-3-9', 1 union
select 1, '2013-3-11', null union
select 1, '2013-3-12', null union
select 1, '2013-3-14', 1 union
select 1, '2013-3-15', 1 union
select 1, '2013-3-16', 1 union
select 1, '2013-3-18', null union
select 2, '2013-3-1', null union
select 2, '2013-3-2', null union
select 2, '2013-3-4', null union
select 2, '2013-3-6', 1 union
select 2, '2013-3-7', 1 union
select 2, '2013-3-8', 1 union
select 2, '2013-3-9', 1 union
select 2, '2013-3-11', 1 union
select 2, '2013-3-12', 1 union
select 2, '2013-3-13', 1 union
select 2, '2013-3-15', null union
select 2, '2013-3-16', null union
select 2, '2013-3-18', 1 union
select 2, '2013-3-19', 1 union
select 2, '2013-3-20', 1 union
select 3, '2013-3-1', null union
select 3, '2013-3-2', null union
select 3, '2013-3-4', 1 union
select 3, '2013-3-5', 1 union
select 3, '2013-3-6', 1 union
select 3, '2013-3-8', null union
select 3, '2013-3-9', null union
select 3, '2013-3-12', 1 union
select 3, '2013-3-13', 1 union
select 3, '2013-3-14', 1 union
select 3, '2013-3-15', 1 union
select 3, '2013-3-18', 1 union
select 3, '2013-3-19', 1 union
select 3, '2013-3-20', 1
go

select eid,
date,
flag,

case when count(*) over( partition by eid, DATEadd( day,- rownum, date)) >= 3
then 1
else null
end '计算出来的flag值' -- 这列和你插入到flag中的值是一样的
from
(
select *,
ROW_NUMBER() over( partition by eid order by date) rownum
from #t
)t
/*
eid date flag 计算出来的flag值
1 2013-03-01 00:00:00.000 NULL NULL
1 2013-03-02 00:00:00.000 NULL NULL
1 2013-03-04 00:00:00.000 NULL NULL
1 2013-03-05 00:00:00.000 NULL NULL
1 2013-03-07 00:00:00.000 1 1
1 2013-03-08 00:00:00.000 1 1
1 2013-03-09 00:00:00.000 1 1
1 2013-03-11 00:00:00.000 NULL NULL
1 2013-03-12 00:00:00.000 NULL NULL
1 2013-03-14 00:00:00.000 1 1
1 2013-03-15 00:00:00.000 1 1
1 2013-03-16 00:00:00.000 1 1
1 2013-03-18 00:00:00.000 NULL NULL
2 2013-03-01 00:00:00.000 NULL NULL
2 2013-03-02 00:00:00.000 NULL NULL
2 2013-03-04 00:00:00.000 NULL NULL
2 2013-03-06 00:00:00.000 1 1
2 2013-03-07 00:00:00.000 1 1
2 2013-03-08 00:00:00.000 1 1
2 2013-03-09 00:00:00.000 1 1
2 2013-03-11 00:00:00.000 1 1
2 2013-03-12 00:00:00.000 1 1
2 2013-03-13 00:00:00.000 1 1
2 2013-03-15 00:00:00.000 NULL NULL
2 2013-03-16 00:00:00.000 NULL NULL
2 2013-03-18 00:00:00.000 1 1
2 2013-03-19 00:00:00.000 1 1
2 2013-03-20 00:00:00.000 1 1
3 2013-03-01 00:00:00.000 NULL NULL
3 2013-03-02 00:00:00.000 NULL NULL
3 2013-03-04 00:00:00.000 1 1
3 2013-03-05 00:00:00.000 1 1
3 2013-03-06 00:00:00.000 1 1
3 2013-03-08 00:00:00.000 NULL NULL
3 2013-03-09 00:00:00.000 NULL NULL
3 2013-03-12 00:00:00.000 1 1
3 2013-03-13 00:00:00.000 1 1
3 2013-03-14 00:00:00.000 1 1
3 2013-03-15 00:00:00.000 1 1
3 2013-03-18 00:00:00.000 1 1
3 2013-03-19 00:00:00.000 1 1
3 2013-03-20 00:00:00.000 1 1
*/