Microsoft SQL Server Cursors

Had to do some sequential merging of records in sql data and this is one of the few occasions when a cursor is useful and it had been quite awhile since I had written a cursor and refreshed my memory with this.

Need to merge records from a table that used to have uniqueness on the Id field to now have uniqueness across StartTime, EndTime, AccountNumber and then merge up the notes into a single record.

Using a merge statement to accomplish this along with the cursor retrieval

DROP TABLE IF EXISTS #FirstTable
CREATE TABLE #FirstTable
(
  Id INT NOT NULL PRIMARY KEY IDENTITY(1,1),
  AccountNumber VARCHAR(10),
  StartTime DATETIME,
  EndTime DATETIME,
  Note VARCHAR(100)
)
INSERT INTO #FirstTable
  (
  AccountNumber,
  StartTime,
  EndTime,
  Note
  )
VALUES
  (
    '12345', -- AccountNumber - varchar(10)
    '2021-01-01', -- StartTime - datetime
    '2021-01-05', -- EndTime - datetime
    'First Note' -- Note varchar(100)
),
  (
    '12345', -- AccountNumber - varchar(10)
    '2021-01-01', -- StartTime - datetime
    '2021-01-05', -- EndTime - datetime,
    'Second Note' -- Note varchar(100)
),
  (
    '54321', -- AccountNumber - varchar(10)
    '2021-02-01', -- StartTime - datetime
    '2021-02-02', -- EndTime - datetime,
    'Yep notes' -- Note varchar(100)
),
  (
    '00001', -- AccountNumber - varchar(10)
    '2021-02-01', -- StartTime - datetime
    '2021-02-06', -- EndTime - datetime,
    NULL
)
DROP TABLE IF EXISTS #RevisedTable;
CREATE TABLE #RevisedTable
(
  AccountNumber VARCHAR(10),
  StartTime DATETIME,
  EndTime DATETIME,
  Note VARCHAR(100)
)
DECLARE @start DATETIME;
DECLARE @end DATETIME;
DECLARE @account VARCHAR(10);
DECLARE @id INT;
DECLARE @note VARCHAR(MAX);
-- declare cursor
DECLARE my_cursor CURSOR FOR
	SELECT Id,
  AccountNumber,
  StartTime,
  EndTime,
  Note
FROM #FirstTable
ORDER BY Id DESC;
-- open cursor
OPEN my_cursor;
FETCH NEXT FROM my_cursor INTO @id, @account, @start, @end, @note;
WHILE @@FETCH_STATUS = 0
BEGIN
  PRINT CONCAT('id: ', @id, 'account: ', @account, ' start: ', @start, ' end: ', @end, ' note:', @note);
  MERGE #RevisedTable AS [target]
	USING (
		VALUES
    (
      @id,
      @account,
      @start,
      @end,
      @note
		)
	) AS [source] (
		Id,
	    AccountNumber,
	    StartTime,
	    EndTime,
	    Note)
	ON (
		[target].[StartTime] = [source].[StartTime] AND
    [target].[EndTime] = [source].[EndTime] AND
    [target].[AccountNumber] = [source].[AccountNumber]
	)
	WHEN NOT MATCHED THEN
		INSERT(AccountNumber,
				StartTime,
				EndTime,
				Note)
		VALUES([source].[AccountNumber],
				[source].[StartTime],
				[source].[EndTime],
				NULLIF(SUBSTRING([source].[Note], 0, 100), ''))
	WHEN MATCHED THEN
		UPDATE SET [target].[Note] = NULLIF(SUBSTRING(CONCAT([target].[Note], ' Id=[' + CAST([source].[Id] as varchar(10)) + ']: ', [source].[Note]), 0, 100), '');
  FETCH NEXT FROM my_cursor INTO @id, @account, @start, @end, @note;
END;
-- close and deallocate cursor
CLOSE my_cursor;
DEALLOCATE my_cursor;

SELECT *
FROM #RevisedTable
ORDER BY AccountNumber

AccountNumber	StartTime	EndTime	Note	CreatedAt
00001	2021-02-01 00:00:00.000	2021-02-06 00:00:00.000	NULL	2021-05-04 15:23:35.780
12345	2021-01-01 00:00:00.000	2021-01-05 00:00:00.000	Second Note Id=[1]: First Note	2021-05-04 15:23:35.780
54321	2021-02-01 00:00:00.000	2021-02-02 00:00:00.000	Yep notes	2021-05-04 15:23:35.780

SELECT *
FROM #FirstTable
ORDER BY AccountNumber

Id	AccountNumber	StartTime	EndTime	Note
4	00001	2021-02-01 00:00:00.000	2021-02-06 00:00:00.000	NULL
1	12345	2021-01-01 00:00:00.000	2021-01-05 00:00:00.000	First Note
2	12345	2021-01-01 00:00:00.000	2021-01-05 00:00:00.000	Second Note
3	54321	2021-02-01 00:00:00.000	2021-02-02 00:00:00.000	Yep notes