Query to find ranges of consecutive rows - sql

Question

I have file that contains a dump of a SQL table with 2 columns: int ID (auto increment identity field) and bit Flag. The flag = 0 means a record is good and the flag = 1 means a record is bad (contains an error). The goal is to find all blocks of consecutive bad records (with flag value of 1) with 1,000 or more rows. The solution shouldn't use cursors or while loops and it should use the set-based queries only (selects, joins etc).
We would like to see the actual queries used and the results in the following format:
StartID – EndID NumberOfErrorsInTheBlock
StartID – EndID NumberOfErrorsInTheBlock
……………………….
StartID – EndID NumberOfErrorsInTheBlock
For example if our data were only 30 records and we were looking for blocks with 5 or more records then the results would look as follows (see the screenshot below, the errors blocks that met the criteria are highlighted) :
[ID Range].....[Number of errors in the block]
11-15..... 5
19-25..... 7
sql file containing sample rows, dropbox

Answer 1

T-SQL Solution for SQL Server 2012 and Above
IF OBJECT_ID('tempdb..#tbl_ranges') IS NOT NULL
DROP TABLE #tbl_ranges;
CREATE TABLE #tbl_ranges
(
row_num INT PRIMARY KEY,
ID INT,
Flag BIT,
Label TINYINT
);
WITH cte_yourTable
AS
(
SELECT Id,
Flag,
CASE
--label min
WHEN Flag != LAG(flag,1) OVER (ORDER BY ID) THEN 1
--inner
WHEN Flag = LAG(flag,1) OVER (ORDER BY ID) AND Flag = LEAD(flag,1) OVER (ORDER BY ID) THEN 2
--end
WHEN Flag = LAG(flag,1) OVER (ORDER BY ID) AND Flag != LEAD(flag,1) OVER (ORDER BY ID) THEN 3
END label
FROM yourTable
)
INSERT INTO #tbl_ranges
SELECT ROW_NUMBER() OVER (ORDER BY ID) row_num,
ID,
Flag,
label
FROM cte_yourTable
WHERE label != 2;
SELECT A.ID ID_start,
B.ID ID_end,
B.ID - A.ID range_cnt
FROM #tbl_ranges A
INNER JOIN #tbl_ranges B
ON A.row_num = B.row_num - 1
AND A.Flag = B.Flag;
IF OBJECT_ID('tempdb..#tbl_ranges') IS NOT NULL
DROP TABLE #tbl_ranges;
Abbreviated Results:
ID_start ID_end range_cnt
----------- ----------- -----------
2 3 1
5 8 3
9 10 1
11 35 24
36 356 320
357 358 1
359 406 47
...

Answer 2

With out using Temp Table, This is the best solution, Here is the Answer and It is perfect example for CTE with in CTE ( Nested CTE )
With Evaluation (ID,Flag,Evaluate)
as
(select ID,Flag,Evaluate = ID-row_number() over (order by Flag,ID)
from [dbo].[SqltestRecordsNew]
where Flag = 1
),
Evaluation_Final (StartingRecordID,EndRecordID,Flag,cnt)
as
(
select min(ID) as StartingRecordID,max(ID) as EndRecordID,
Flag, cnt = count(*)
from Evaluation
group by Evaluate, Flag
)
select Concat(StartingRecordID,' - ', EndRecordID) as 'StartingRecordID - EndRecordId',
cnt as GroupItemCnt from Evaluation_Final
where cnt > 999
order by Concat(StartingRecordID,' - ', EndRecordID)
-- Test results Case 1
Select ID,Flag,
Case when Flag=1 then 'Success'
else 'Defect Data'
End as TestResults
from SqltestRecordsNew
where ID between 1494363 and 1495559
-- Test results Case 2
Select ID,Flag,
Case when Flag=1 then 'Success'
else 'Defect Data'
End as TestResults from SqltestRecordsNew
where ID between 1498409 and 1503899
-- Test results Case 3
Select ID,Flag,
Case when Flag=1 then 'Success'
else 'Defect Data'
End as TestResults from SqltestRecordsNew
where ID between 1548257 and 1550489