SQL Update with CTEs not updating records - sql

Question

I am attempting to update a set of records that are duplicates in three particular columns. The reason for this update is that there is a conflict when trying to insert this data into an updated database schema. The conflict is caused by a new constraint that has been added on DM_ID, DM_CONTENT_TYPE_ID, and DMC_TYPE. I need to adjust the DM_CONTENT_TYPE_ID column to either 1, 3, or 5 based on the row number to get around this. A sample of the duplicate data looks as such. Notice that the first three columns are the same.
+--------+--------------------+----------+--------------------------------------+
| DM_ID | DM_CONTENT_TYPE_ID | DMC_TYPE | DMC_PATH |
+--------+--------------------+----------+--------------------------------------+
| 314457 | 1 | TIF | \\DOCIMG\CD\1965\19651227\7897-0.tif |
| 314457 | 1 | TIF | \\DOCIMG\DR\640\0001_640_0001.tif |
| 314458 | 1 | TIF | \\DOCIMG\CD\1965\19651227\7898-0.tif |
| 314458 | 1 | TIF | \\DOCIMG\TD\640\0002_640_0001.tif |
| 314460 | 1 | TIF | \\DOCIMG\CD\1965\19651227\7900-0.tif |
| 314460 | 1 | TIF | \\DOCIMG\ZZ\640\0003_640_0003.tif |
| 314461 | 1 | TIF | \\DOCIMG\CD\1965\19651227\7901-0.tif |
| 314461 | 1 | TIF | \\DOCIMG\ED\6501\03_0001.tif |
| 314461 | 1 | TIF | \\DOCIMG\ZZ\640\0004_640_0004.tif |
+--------+--------------------+----------+--------------------------------------+
This is the desired output to get around the constraint issue:
+--------+--------------------+----------+--------------------------------------+
| DM_ID | DM_CONTENT_TYPE_ID | DMC_TYPE | DMC_PATH |
+--------+--------------------+----------+--------------------------------------+
| 314457 | 1 | TIF | \\DOCIMG\CD\1965\19651227\7897-0.tif |
| 314457 | 3 | TIF | \\DOCIMG\DR\640\0001_640_0001.tif |
| 314458 | 1 | TIF | \\DOCIMG\CD\1965\19651227\7898-0.tif |
| 314458 | 3 | TIF | \\DOCIMG\TD\640\0002_640_0001.tif |
| 314460 | 1 | TIF | \\DOCIMG\CD\1965\19651227\7900-0.tif |
| 314460 | 3 | TIF | \\DOCIMG\ZZ\640\0003_640_0003.tif |
| 314461 | 1 | TIF | \\DOCIMG\CD\1965\19651227\7901-0.tif |
| 314461 | 3 | TIF | \\DOCIMG\ED\6501\03_0001.tif |
| 314461 | 5 | TIF | \\DOCIMG\ZZ\640\0004_640_0004.tif |
+--------+--------------------+----------+--------------------------------------+
The script I have developed is as such:
;WITH CTE AS
(SELECT -- Grab the documents that have a duplicate.
DM_ID
,DM_CONTENT_TYPE_ID
,DMC_TYPE
,COUNT(*) 'COUNT'
FROM
[DM_CONTENT]
GROUP BY
DM_ID
,DM_CONTENT_TYPE_ID
,DMC_TYPE
HAVING
COUNT(*) > 1),
CTE2 AS
(SELECT -- Designate the row number for the duplicate documents.
DMC.*
,ROW_NUMBER() OVER(PARTITION BY DMC.DM_ID, DMC.DM_CONTENT_TYPE_ID, DMC.DMC_TYPE ORDER BY DMC.DMC_PATH) AS 'ROWNUM'
FROM
[DM_CONTENT] DMC
JOIN CTE
ON DMC.DM_ID = CTE.DM_ID),
CTE3 AS
(SELECT -- Set the new document type ID based on the row number.
*
,CASE
WHEN ROWNUM = 1
THEN 1
WHEN ROWNUM = 2
THEN 3
WHEN ROWNUM = 3
THEN 5
END AS 'DM_CONTENT_TYPE_ID_NEW'
FROM
CTE2)
UPDATE -- Update the records.
DMC
SET
DMC.DM_CONTENT_TYPE_ID = CTE3.DM_CONTENT_TYPE_ID_NEW
FROM
[DM_CONTENT] DMC
JOIN CTE3
ON DMC.DM_ID = CTE3.DM_ID
Now when I execute the script, it says that the appropriate rows have been affected. However, when I check the [DM_CONTENT] table, the DM_CONTENT_TYPE_ID actually hasn't been updated and still remains at a value of 1. If I SELECT from CTE3, the DM_CONTENT_TYPE_ID_NEW, is the appropriate new ID. My logic seems to be sound, but I cannot figure out what mistake I am making. Does anyone have any insight? Thanks in advance!

Answer 1

This seems much simpler to write as:
WITH toupdate AS (
SELECT DMC.*,
ROW_NUMBER() OVER (PARTITION BY DMC.DM_ID, DMC.DM_CONTENT_TYPE_ID, DMC.DMC_TYPE
ORDER BY DMC.DMC_PATH) AS ROWNUM
FROM DM_CONTENT DMC
)
UPDATE toupdate
SET DM_CONTENT_TYPE_ID = (CASE ROWNUM WHEN 2 THEN 3 WHEN 3 THEN 5 END)
WHERE ROWNUM > 1;
Now, I find it suspicious that your join conditions are only on DM_ID. I think the problem is that you are getting multiple matches between the CTE and your table. An arbitrary match is used for the update -- and that happens to be the first one encountered (hence a value of 1).

Answer 2

Try
UPDATE CTE3
SET DM_CONTENT_TYPE_ID = DM_CONTENT_TYPE_ID_NEW
instead of what you're currently doing.
Updating from a CTE works a little different that regular table joins.

Answer 3

Should work with any no. of duplicates. Try this way
;WITH cte
AS (SELECT Row_number()
OVER(
partition BY dm_id, dm_content_type_id, dmc_type
ORDER BY DMC_PATH) AS Rn,
*
FROM dm_content)
UPDATE cte
SET dm_content_type_id = rn + (rn -1)