How to create loop based on value of row? - sql

Question

I have problem when I use my query bellow to have a looping inside the cursor.
data in table1 will be like this:
id | data
----|---------
A | 4
B | 2
C | 5
the result in table2 should be like this:
id | data
----|---------
A | 1
A | 1
A | 1
A | 1
B | 1
B | 1
C | 1
C | 1
C | 1
C | 1
C | 1
I have SQL query with cursor like this:
DECLARE #table2 table ( id VARCHAR(500), data INTEGER)
DECLARE Cur CURSOR FOR
SELECT id, data FROM table1
OPEN Cur
WHILE ( ##FETCH_STATUS = 0 )
BEGIN
DECLARE #LoopNum INTEGER
DECLARE #tempID VARCHAR(255)
DECLARE #tempDATA INTEGER
FETCH NEXT FROM Cur INTO #tempID, #tempDATA
set #LoopNum = 0
WHILE #LoopNum < #tempDATA
BEGIN
INSERT INTO table2 (id, data)
VALUES( #tempID, 1)
SET #LoopNum = #LoopNum + 1
END
END
CLOSE Cur
DEALLOCATE Cur
SELECT * FROM table2
but the query didn't work. is there something wrong with my query?
Thank you.

Answer 1

Use this query to the expected result.
CREATE TABLE #test
(id CHAR(1),data INT)
INSERT #test VALUES ('A',4)
INSERT #test VALUES('B',2)
INSERT #test VALUES('C',5);
SELECT s.id, 1 AS data
FROM #test s
INNER JOIN
master.dbo.spt_values t ON t.type='P'
AND t.number BETWEEN 1 AND s.data
Note: Refer this Why (and how) to split column using master..spt_values?

Answer 2

You actually don't need a loop
IF OBJECT_ID('TEMPDB..#TEMP') IS NOT NULL
DROP TABLE #TEMP
SELECT 'A' AS ID, 4 AS DATA
INTO #TEMP UNION
SELECT 'B', 2 UNION
SELECT 'C', 5
;WITH CTE AS
(
SELECT 1 AS NUMBER
UNION ALL
SELECT NUMBER + 1
FROM CTE
WHERE NUMBER < 100
)
SELECT T.ID, 1
FROM CTE C
INNER JOIN #TEMP T
ON C.NUMBER <= T.DATA
ORDER BY T.ID
Carefull that if you want ot generate a large set of numbers in the CTE it may become slower.

Answer 3

Use a Recursive CTE which will help you to loop through the records.
CREATE TABLE #test
(id CHAR(1),data INT)
INSERT #test
VALUES ('A',4),('B',2),('C',5);
WITH cte
AS (SELECT 1 AS da,id,data
FROM #test a
UNION ALL
SELECT da + 1,id,data
FROM cte a
WHERE da < (SELECT data
FROM #test b
WHERE a.id = b.id))
SELECT id,
1 AS data
FROM cte
ORDER BY id

Answer 4

i used two loops
1. for each row
2. for number for duplicate insert
SET NOCOUNT on;
DECLARE #t table(row int IDENTITY(1,1),id varchar(10),data int)
INSERT INTO #t
SELECT * from xyz
DECLARE #x table(id varchar(10),data int) --table to hold the new data
DECLARE #i int=(SELECT count (*) from xyz) --number of rows main table
DECLARE #y int --number of duplicate
DECLARE #p int=1 --number of rows
WHILE #i!=0 --loop until last row of main table
BEGIN
SET #y=(SELECT data FROM #t WHERE row=#p) --set #y for number of 'row duplicate'
WHILE #y!=0
BEGIN
INSERT INTO #x
SELECT id,1
FROM #t
WHERE row=#p
SET #y=#y-1
END
SET #p=#p+1
SET #i=#i-1
END
SELECT * FROM #x