sql query - select duplicates within a 12 hour period - sql

Question

if i have data as follows
A | 01/01/2008 00:00:00
B | 01/01/2008 01:00:00
A | 01/01/2008 11:59:00
C | 02/01/2008 00:00:00
D | 02/01/2008 01:00:00
D | 02/01/2008 20:00:00
I want to only select the records whose identifiers (A, B, C or D) have occured twice within a 12 hour period. In this example above this would only be 'A'
Can anyone help please (this is for an Oracle data base)
Thanks
M

Answer 1

Select Distinct A.Identifer
From Table A
Join Table B -- EDIT to eliminate self Joins (to same row)
On A.PrimKey <> B.PrimaryKey
And A.Identifer = B.Identifer
-- EDIT to fix case where 2 at same time
And A.OccurTime >= B.OccurTime
And A.OccurTime < B.OccurTime + .5
and to implement question asked in comment,
(Ignoring records which are on different days)
-- for SQL Server,
Select Distinct A.Identifer
From Table A
Join Table B
On A.PrimKey <> B.PrimaryKey
And A.Identifer = B.Identifer
-- EDIT to fix case where 2 at same time
And A.OccurTime >= B.OccurTime
And A.OccurTime < B.OccurTime + .5
Where DateDiff(day, A.OccurTime, B.OccurTime) = 0
-- or for oracle...
Select Distinct A.Identifer
From Table A
Join Table B
On A.PrimKey <> B.PrimaryKey
And A.Identifer = B.Identifer
-- EDIT to fix case where 2 at same time
And A.OccurTime >= B.OccurTime
And A.OccurTime < B.OccurTime + .5
Where Trunc(A.OccurTime) = Trunc(B.OccurTime)

Answer 2

Select
A.Id
From
YourTable A
Where
A.YourDateTime Between :StartDateTime and :EndDateTime
Group By
A.Id
Having
COUNT(A.Id) = 2

Answer 3

I haven't checked William's query but I would seriously consider using what he has over every other. Analytics are da bomb. Anytime you find yourself joining a table back to itself is virtually guaranteed to be an opportunity to use analytics and will out perform the query with one table referenced twice every time.
You'll be amazed how much faster the analytic solution will be.

Answer 4

SELECT identifier
FROM table_name outer
WHERE EXISTS( SELECT 1
FROM table_name inner
WHERE inner.identifier = outer.identifier
AND inner.date_column BETWEEN outer.date_column AND outer.date_column + interval '12' hour
AND inner.rowid != outer.rowid )

Answer 5

I'm not 100% sure of your requirements, however this might give you some ideas about how to do what you need. For example you said exactly 2; what if there are 3 occurances? etc.
create table t (ident varchar2(16), occurance timestamp);
insert into t (ident, occurance) values ('a', to_date('20080101000000', 'yyyymmddhh24miss'));
insert into t (ident, occurance) values ('b', to_date('20080101010000', 'yyyymmddhh24miss'));
insert into t (ident, occurance) values ('a', to_date('20080101115900', 'yyyymmddhh24miss'));
insert into t (ident, occurance) values ('c', to_date('20080102000000', 'yyyymmddhh24miss'));
insert into t (ident, occurance) values ('d', to_date('20080102010000', 'yyyymmddhh24miss'));
insert into t (ident, occurance) values ('d', to_date('20080102200000', 'yyyymmddhh24miss'));
insert into t (ident, occurance) values ('d', to_date('20080103020000', 'yyyymmddhh24miss'));
select ident, occurance
from
(
select ident, occurance,
lag(occurance) over (partition by ident order by occurance) previous,
lead(occurance) over (partition by ident order by occurance) next
from t
)
where
((occurance-previous<interval'12:00' hour to minute and extract(day from occurance) = extract(day from previous))
or (next-occurance<interval'12:00' hour to minute and extract(day from occurance) = extract(day from next)))
/

Answer 6

SELECT namecol FROM tbl A
WHERE EXISTS (
SELECT 1 from tbl B
WHERE b.namecol = a.namecol
AND b.timestamp > a.timestamp
AND b.timestamp - 0.5 <= a.timestamp )