Row By Row ( Without Cursor or Loops) - sql

Question

Here I have sample data of students having RollNumbers and their coursecodes.
-------------------------
Roll CourseCode
--------------------------
1011 CS201
2213 CS201
3312 CS101
4000 CS201
1011 CS101
5312 ME102
1011 PT101
3312 ME102
Result should be Coursecode and their exam date
e.g (Sort Out Distinct Coursecodes)
First I am picking CS201 and assigning that coursecode a date; placing it in a temporary table,then I picked CS101 and will check in temporary table whether the RollNumbers of this Coursecode matches any other RollNumber of other Coursecode in the temporary table.
---------------------
Code Date
---------------------
CS101 1
CS201 2
ME102 1
PT101 3
My code:
#temp3 contains all data (CourseCodes, RollNumbers)
#mytemp1 ( Output Data)
and cursor contains the Distinct coursecodes
SET #cursor = CURSOR FOR
SELECT DISTINCT coursecode
FROM #temp3
ORDER BY CourseCode
OPEN #cursor
FETCH NEXT
FROM #cursor INTO #cursorid
WHILE ##FETCH_STATUS = 0
BEGIN
BEGIN
SET #j=1
WHILE(#j !=9999999)
BEGIN
IF( SELECT COUNT(*) FROM #temp3 WHERE CourseCode = #cursorid AND RegdNo IN (
SELECT RegdNo FROM #temp3 WHERE CourseCode IN ( SELECT coursecode FROM #myTemp1 WHERE counter1 = #j)
)) = 0
BEGIN
INSERT INTO #myTemp1 VALUES (#cursorid,#j)
SET #j=9999999
END
ELSE
BEGIN
SET #j = #j + 1
END
END
END
FETCH NEXT
FROM #cursor INTO #cursorid
END
CLOSE #cursor
DEALLOCATE #cursor
This code is working fine but taking too much time( 4110222 records)
Any help would be appreciated

Answer 1

Here is some code. I believe that you have error in output and CS101 should precede CS201:
DECLARE #t TABLE ( Roll INT, Code CHAR(5) )
INSERT INTO #t
VALUES ( 1011, 'CS201' ),
( 2213, 'CS201' ),
( 3312, 'CS101' ),
( 4000, 'CS201' ),
( 1011, 'CS101' ),
( 5312, 'ME102' ),
( 1011, 'PT101' ),
( 3319, 'ME102' );
WITH cte1
AS ( SELECT code ,
ROW_NUMBER() OVER ( ORDER BY Code ) AS rn
FROM #t
GROUP BY code
),
cte2
AS ( SELECT code ,
rn ,
1 AS Date
FROM cte1
WHERE rn = 1
UNION ALL
SELECT c1.code ,
c1.rn ,
CASE WHEN EXISTS ( SELECT *
FROM #t a
JOIN #t b ON a.Roll = b.Roll
JOIN cte1 c ON c.rn < c1.rn
AND b.Code = c.code
WHERE a.code = c1.code ) THEN 1
ELSE 0
END
FROM cte1 c1
JOIN cte2 c2 ON c1.rn = c2.rn + 1
),
cte3
AS ( SELECT Code ,
CASE WHEN Date = 0 THEN 1
ELSE SUM(Date) OVER ( ORDER BY rn )
END AS Date
FROM cte2
)
SELECT * FROM cte3
Output:
Code Date
CS101 1
CS201 2
ME102 1
PT101 3
EDIT:
cte1 will return:
code rn
CS101 1
CS201 2
ME102 3
PT101 4
The main work is done in cte2. It is recursive common table expression.
First you take top 1 row from cte1:
SELECT code ,
rn ,
1 AS Date
FROM cte1
WHERE rn = 1
Then the recursion progresses:
You are joining cte1 on cte2 and pick following rns (2, 3...) and check if there are any rolls in CS201 that match rolls in previous codes(CS101) in first step, check if there any rolls in ME102 that match rolls in previous codes(CS101, CS201) in second step etc. If exists you return 1 else 0:
code rn Date
CS101 1 1
CS201 2 1
ME102 3 0
PT101 4 1
Last cte3 does the following: if Date = 0 then return 1, else return sum of Dates in previous rows including current row.
EDIT1:
Since my understanding was incorrect here is one more statement:
WITH cte
AS ( SELECT code ,
ROW_NUMBER() OVER ( ORDER BY Code ) AS rn
FROM #t
GROUP BY code
)
SELECT co.Code,
DENSE_RANK() OVER(ORDER BY ISNULL(o.Code, co.Code)) AS Date
FROM cte co
OUTER APPLY(SELECT TOP 1 ci.Code
FROM cte ci
WHERE ci.rn < co.rn AND
NOT EXISTS(SELECT * FROM #t
WHERE code = ci.code AND
roll IN(SELECT roll FROM #t WHERE code = co.code)) ORDER BY ci.rn) o
ORDER BY co.rn
Output:
Code Date
CS101 1
CS201 2
ME102 1
PT101 2
EDIT2:
This is insane but, here is code that seems to work:
WITH cte
AS ( SELECT * ,
ROW_NUMBER() OVER ( PARTITION BY roll ORDER BY Code ) AS Date
FROM #t
)
SELECT Code ,
MAX(Date) AS Date
FROM cte
GROUP BY Code