Question

I have a table that looks like this:

Id (PK, int, not null)
ReviewedBy (nvarchar(255), not null)
ReviewDateTime(datetime, not null)
Decision_id (int, not null)
Item_id (FK, int, not null)

The business process with this table is that each Item (shown by Item_id foreign key) is to be worked on by 2 people.

How can I query this table to determine who (ReviewedBy) reviewed the item first and who reviewed it second.

I’m really struggling to figure this out because I neglected adding a Type column to my table that would determine which the user was acting as. 🙁

Edit

Given the following data

Id,ReviewedBy,ReviewedWhen,SomeOtherId,
16,111111,2011-12-14 22:06:54,1,
17,187935,2011-12-14 22:07:03,1,
18,187935,2011-12-14 22:07:18,2,
19,187935,2011-12-14 22:07:20,3,
20,111111,2011-12-14 22:07:23,2,
21,187935,2011-12-14 22:07:26,3,
22,123456,2011-12-14 22:27:50,4,

with schema

CREATE TABLE [Reviews] (
[Id] INTEGER  NOT NULL PRIMARY KEY AUTOINCREMENT,
[ReviewedBy] NVARCHAR(6)  NOT NULL,
[ReviewedWhen] TIMESTAMP DEFAULT CURRENT_TIMESTAMP NOT NULL,
[SomeOtherId] INTEGER  NOT NULL
);

Executing the following to get a list of people who did second reviews will return rows where there is only one review for SomeOtherId.

select t1.*
from Reviews as t1
  left outer join Reviews as t2
    on (t1.SomeOtherId = t2.SomeOtherId and t1.ReviewedWhen < t2.ReviewedWhen)
where t2.SomeOtherId is null;

Solution

-- First checks
select t1.ReviewedBy, count(t1.Id)
from Reviews as t1
  left outer join Reviews as t2
    on (t2.SomeOtherId = t1.SomeOtherId and t1.ReviewedWhen > t2.ReviewedWhen)
where          t2.SomeOtherID is null
group by t1.ReviewedBy;

-- Second checks
select t1.ReviewedBy, count(t1.Id)
from Reviews as t1
  left outer join Reviews as t2
    on (t2.SomeOtherId = t1.SomeOtherId and t1.ReviewedWhen < t2.ReviewedWhen)
where          t2.SomeOtherID is null
and  t1.Id not in (select Id from Reviews group by SomeOtherId having count(SomeOtherId) = 1)
group by t1.ReviewedBy;

Essentially, it was counting items where there was only one review as both a first and second check. All I had to do was ensure that when I’m counting second checks that I’m not including rows with only one review.

I thought I could achieve this in one query but guess not.

Answer 1

Try this:

select 
t1.ReviewedBy FirstReviewer,
t2.ReviewedBy SecondReviewer
from
Table t1
left outer join Table t2 on t1.Item_Id = t2.Item_Id and t2.ReviewDateTime > t1.ReviewDateTime

If you want to only return rows that have been reviewed by two people, change the left outer join to an inner join.

If ReviewDateTime is never updated and Id is an identity column you can change the join to join on Id rather ReviewDateTime, which will be faster.