T-SQL Identifying gaps in broken sequence of dates

user_2032414 0
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Please can you help with a problem I am having, I believe is related to the gaps and islands problem in T-SQL. I am using SQL Server 2014.

I am trying to identify count the number of consecutive occurrences of a table/index combination using a date column to distinguish between the broken chains.

Please see the below T-SQL to demonstrate what I am trying to achieve, in particular how do I calculate the Rnk column which for demo purposes I have manually hard-coded?

CREATE TABLE #test (RowID INT IDENTITY(1,1), FileDate DATE, TableName VARCHAR(100), IndexName VARCHAR(100), Rnk INT)

INSERT INTO #test (FileDate, TableName, IndexName, Rnk) 
VALUES
('2015-10-31', 't1', 'idx1', 1),
('2015-10-30', 't1', 'idx1', 2),

('2015-10-27', 't1', 'idx1', 1),
('2015-10-26', 't1', 'idx1', 2),
('2015-10-25', 't1', 'idx1', 3),

('2015-10-23', 't1', 'idx1', 1),
('2015-10-22', 't1', 'idx1', 2),
('2015-10-21', 't1', 'idx1', 3),
('2015-10-20', 't1', 'idx1', 4),
('2015-10-19', 't1', 'idx1', 5),
('2015-10-15', 't1', 'idx1', 1),
('2015-10-13', 't1', 'idx1', 1),
('2015-10-10', 't1', 'idx1', 1),
('2015-10-09', 't1', 'idx1', 2),

('2015-10-27', 't3', 'idx13', 1),
('2015-10-26', 't3', 'idx13', 2),
('2015-10-25', 't3', 'idx15', 1),
('2015-10-24', 't3', 'idx15', 2),
('2015-10-21', 't3', 'idx13', 1)

SELECT * FROM #test 

DROP TABLE #test

In the screenshot I've attached, the portion of results highlighted would show I want the Rnk column to sequence the consecutive appearance of t1/idx between 2015-10-27 - 2015-10-25, but reset the number for the next appearance at 2015-10-23 through to 2015-10-19.

Can anyone assist me please?

IMG1

Thanks.

gaps-and-islands sequence tsql sql-server
3 Answers

Subtract a sequence of numbers from the date -- and the groups you have identified will have a constant value. Then you can use row_number():

select t.*,
       row_number() over (partition by tablename, indexname,
                                       dateadd(day, - seqnum, filedate)
                          order by filedate desc
                         ) as rnk
from (select t.*,
             row_number() over (partition by tablename, indexname order by filedate) as seqnum
      from t
     ) t
user_11440350

I would use cumulative approach :

select t.FileDate, t.TableName, t.IndexName,
       row_number() over (partition by tablename, indexname, grp order by rowid)
from (select t.*, sum(case when gap > 1 then 1 else 0 end) over (partition by tablename, indexname order by rowid) as grp
      from (select t.*, 
                   isnull(datediff(day, filedate, lag(filedate) over (partition by tablename, indexname order by rowid)), 1) as gap
            from #test t
           ) t
     ) t;
user_55294450

Similar to the answer from Yogesh, who beat me to it.
(hint: don't expect to be faster when typing an answer on your phone)

SELECT 
RowID, FileDate, TableName, IndexName, 
ROW_NUMBER() OVER (PARTITION BY TableName, IndexName,  DateRank ORDER BY FileDate DESC) AS Rnk
FROM
(
  SELECT *,
  SUM(DateGap) OVER (PARTITION BY TableName, IndexName ORDER BY FileDate DESC) AS DateRank
  FROM
  (
      SELECT RowID, FileDate, TableName, IndexName,
      --  Rnk as ExpRnk,
      CASE WHEN DATEDIFF(DAY, FileDate, LAG(FileDate) OVER (PARTITION BY TableName, IndexName ORDER BY FileDate DESC)) <= 1 THEN 0 ELSE 1 END AS DateGap
      FROM #Test
  ) q1
) q2
ORDER BY RowID;
user_40034190
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