Check the below input data and expected output to fill the gap of missing codes.

Input Data:

Code
----
A
NULL
NULL
NULL
NULL
NULL
M
NULL
NULL
NULL
N
NULL
NULL

Expected Output:

OldCode NewCode
------- -------
A       A
NULL    A
NULL    A
NULL    A
NULL    A
NULL    A
M       M
NULL    M
NULL    M
NULL    M
N       N
NULL    N
NULL    N

Create a table with sample data:

CREATE TABLE MissingData
(
	Code CHAR(1)
)
GO
 
INSERT INTO MissingData
CodeS ('A'),(NULL),(NULL),(NULL),(NULL),(NULL)
,('M'),(NULL),(NULL),(NULL),('N'),(NULL),(NULL)
GO

Solution:

;WITH CTE AS
(
       SELECT p.Code
       ,ROW_NUMBER() OVER (ORDER BY (SELECT 1)) rrnk FROM MissingData p 
) 
SELECT
       c.Code AS OldCode
       ,(
          SELECT d.Code from CTE d WHERE d.rrnk = (Select max(e.rrnk) from CTE e 
          Where e.rrnk <= c.rrnk and (e.Code != '' ))
       ) NewCode
FROM CTE c

Please try the different solution for this puzzle and share it via comment...

In this post, I will give you one full demo to find a missing number of identity column in SQL Server.

Before a few days ago, I was working on production report and found that some number is missing. This sequence and missing number are very important.
Immediately one requirement come to my desk is, please find a list of all missing number for investigation purpose.

Below is a full demo script to find the missing number in SQL Server.

First Create one sample table with data.

/*Create one table to store Numbers*/

CREATE TABLE dbo.tbl_Numbers
(
	ID INTEGER
)
GO

/*Insert some test records. You can also see I have missed many number which we are going to find by query*/

INSERT INTO dbo.tbl_Numbers 
VALUES(1),(2),(3),(4),(6),(7),(9),(10)
,(11),(15),(16),(19),(22),(23),(24)
,(28),(32),(33),(34),(35),(38),(40)
,(41),(42),(43),(44),(45),(47),(49)
,(50)
GO

Below is step by step script to find this missing number.

/*Step 1: Create one temp table and store all distinct Numbers*/
SELECT DISTINCT ID INTO #DistinctID FROM dbo.tbl_Numbers
GO

/*Step 2: Find NextID which has something missing before it.
Store into one TempTable*/

SELECT 
	(ROW_NUMBER()OVER (ORDER BY ID ASC)) AS TableCountID
	,b.ID 
	,(
		SELECT Top 1 ID
		FROM #DistinctID a WITH (NOLOCK)
		WHERE a.ID > b.ID
	) AS NextID
INTO #NextID
FROM #DistinctID AS b WITH (NOLOCK)
WHERE 
(
	SELECT Top 1 ID
	FROM #DistinctID a WITH (NOLOCK)
	WHERE a.ID > b.ID
) <> b.ID+1
ORDER BY b.ID

/*Step 3: Create one temp table to store missing number details */

CREATE TABLE #MissingID
(
	TableCountID INTEGER
	,ID INTEGER
	,NextID INTEGER
	,MissingID INTEGER
	,TotalDiff INTEGER
)
GO

/*Step 4: Now start to find missing id using WHILE Loop. */

DECLARE @CountID INTEGER
DECLARE @InnerLoopCountID INTEGER
SET @CountID = 1
WHILE (@CountID &gt; 0)
BEGIN
INSERT INTO #MissingID
SELECT 
	TableCountID
	,ID 
	,NextID
	,CASE WHEN TotalDiff = 1 THEN ID+TotalDiff END AS MissingID
	,TotalDiff		
FROM
(
SELECT	
	TableCountID
	,ID
	,NextID
	,(NextID-ID)-1 AS TotalDiff
FROM #NextID
) AS T WHERE TableCountID = @CountID

IF ((SELECT (NextID-ID)-1 FROM #NextID WHERE TableCountID = @CountID)&gt;1)
BEGIN	
	SET @InnerLoopCountID = (SELECT (NextID-ID)-1 FROM #NextID WHERE TableCountID = @CountID)
	
WHILE (@InnerLoopCountID &gt; 0)
BEGIN
	INSERT INTO #MissingID
	SELECT 
		TableCountID
		,ID 
		,NextID
		,ID+@InnerLoopCountID AS MissingNumber
		,TotalDiff		
	FROM
	(
	SELECT	
		TableCountID
		,ID
		,NextID
		,(NextID-ID)-1 AS TotalDiff
	FROM #NextID
	) AS T WHERE TableCountID = @CountID		

	SET @InnerLoopCountID = @InnerLoopCountID - 1				
END			
END
SET @CountID = @CountID+1

IF @CountID = (SELECT COUNT(1)+1 FROM #NextID)
BEGIN	
	RETURN
END
END
GO

/*Step 5: Now select missing data from #MissingID temp table. 
You can find full details on MissingID.*/

SELECT *FROM #MissingID WHERE MissingID IS NOT NULL ORDER BY MissingID 
GO

Result of Step 5:In the above result you can find total 20 missing number. MissingID Column represents missing numbers.