SQL Server : loop through every row, add incremented value to column - sql

Question

I have just added a new column, Person_Id_Helper to MyTable. It is supposed to contain 1,2,3 etc, in the order the table is now sorted.
This is what I want to do:
DECLARE #i INT = 1, #NumberOfRows INT = SELECT COUNT(*) FROM MyTable
WHILE(#i <= #NumberOfRows)
BEGIN
-- Person_Id_Helper = #i
-- #i = #i + 1
END
How do I write this?

Answer 1

I think, that it might be the wrong idea to persist the sort oder within a column. But - for sure! - it is the wrong idea to do this in a while loop.
Read about row-based and set-based approaches. SQL demands for set-based thinking...
Look at this as an example how to do this (just paste it into an empty query window and execute, adapt to your needs):
DECLARE #tbl TABLE(SortDate DATE, Inx INT);
INSERT INTO #tbl VALUES({d'2016-01-20'},0)
,({d'2016-01-19'},0)
,({d'2016-01-14'},0)
,({d'2016-01-16'},0);
WITH cte AS
(
SELECT Inx,ROW_NUMBER() OVER(ORDER BY SortDate) AS RN
FROM #tbl
)
UPDATE cte SET Inx=RN;
SELECT * FROM #tbl;

Answer 2

I think this is what you want to achieve -
DECLARE #i INT = 0
UPDATE MyTable
SET
#i = Person_Id_Helper = #i + 1
Now check your column value.
Well we can not use ORDER BY clause in update statement. But to use it here is the updated query.
UPDATE t
SET Person_Id_Helper = rn.RowNum
FROM MyTable t
INNER JOIN (SELECT
ID
,ROW_NUMBER() OVER (ORDER BY ID) AS RowNum
FROM MyTable) rn
ON t.ID = rn.ID
#shungo: Thanks for point out.

Answer 3

Try like this,
DECLARE #tbl TABLE
(
datecolumn DATE,
Person_Id_Helper INT
);
INSERT INTO #tbl
VALUES ({d'2016-01-20'},
0),
({d'2016-01-19'},
0),
({d'2016-01-14'},
0),
({d'2016-01-16'},
0);
SELECT *
FROM #tbl;
UPDATE T
SET Person_Id_Helper = rn
FROM (SELECT Person_Id_Helper,
Row_number()
OVER(
ORDER BY datecolumn) AS rn
FROM #tbl) T
SELECT *
FROM #tbl;

Answer 4

Looping add increment the value using cursor in sqlserver
CREATE TABLE [dbo].[Table1](
[PID] [int] NULL,
[ProductDesc] [nvarchar](50) NULL,
[ProductCode] [nvarchar](10) NULL
) ON [PRIMARY]
GO
INSERT [dbo].[Table1] ([PID], [ProductDesc], [ProductCode], [Person_Id_Helper]) VALUES (1, N'Packet-Eye', N'P001', NULL)
GO
INSERT [dbo].[Table1] ([PID], [ProductDesc], [ProductCode], [Person_Id_Helper]) VALUES (2, N'Wiggy', N'W099 ', NULL)
GO
INSERT [dbo].[Table1] ([PID], [ProductDesc], [ProductCode], [Person_Id_Helper]) VALUES (3, N'Wimax-Lite', N'W001', NULL)
GO
INSERT [dbo].[Table1] ([PID], [ProductDesc], [ProductCode], [Person_Id_Helper]) VALUES (4, N'Wimax-Home', N'e W002 ', NULL)
GO
Declare #count int
DECLARE #PID int
set #count=0
DECLARE c1 CURSOR READ_ONLY
FOR
SELECT [PID] FROM [Table1]
OPEN c1
FETCH NEXT FROM c1 INTO #PID
WHILE ##FETCH_STATUS = 0
BEGIN
set #count=#count+1
update Table1 set Person_Id_Helper=#count where [PID]=#PID
FETCH NEXT FROM c1 INTO #PID END
CLOSE c1
DEALLOCATE c1
select * from Table1