Update multiple rows in table from table variable - sql

Question

I'm writing a stored procedure to update multiple records based on a table variable parameter.
The existing table is: Tb_Project_Image with relevant columns:
id PK (identity 1,1)
cat_ord decimal(4,2)
The procedure will receive a temporary table variable (shown in the code below) containing the id as PI_ID, and the new value for cat_ord as newCatOrd. idx is a simple identity for each row containing 1...n where n is the rowcount of #tempTable.
For each row in #tempTable, I want to update Tb_Project_Image where id = PI_ID to the corresponding value.
DECLARE #tempTable table (
idx smallint Primary Key IDENTITY(1,1),
PI_ID bigint,
newCatOrd decimal(4, 2) not null )
INSERT INTO #tempTable values (3, 7.01)
INSERT INTO #tempTable values (4, 7.02)
INSERT INTO #tempTable values (5, 7.03)
--etc...
DECLARE #error int
DECLARE #update int
DECLARE #iter int
SET #iter = 1
BEGIN TRAN
WHILE #iter <= (select COUNT(*) from #tempTable)
BEGIN
UPDATE Tb_Project_Image
SET cat_ord = (SELECT newCatOrd FROM #tempTable
WHERE idx = #iter)
WHERE id = (SELECT PI_ID FROM #tempTable
WHERE idx = #iter)
--error checking
set #error = ##ERROR
set #update = ##ROWCOUNT
IF ((#error = 0) AND (#update = 1))
BEGIN
SET #iter = #iter + 1
CONTINUE
END
ELSE
BREAK
END
IF ((#error = 0) AND (#update = 1))
COMMIT TRAN
ELSE
ROLLBACK TRAN
GO
Now, the error checking is because, to ensure integrity, EACH row in the temporary table MUST make 1 update. (explanation omitted to save space) If a single iteration of the while loop threw an error, or didn't effect exactly 1 row, I want to break the loop and rollback the transaction
THE PROBLEM I'm having is that this error checking is not working. I'm currently running it with 14 rows in #tempTable and the 11th uses a PI_ID not found in the Project_Image table. Therefore, #update = 0... but it continues the loop and commits the data.
I'd be doubly glad if someone had a method of doing this that only used a single update statement.

Answer 1

You cannot do it this way, because even SET resets the state of ##ERROR and ##ROWNUMBER variables. In this case ##ROWCOUNT is set to 1 after set #error = ##ERROR. If you do not assign the values to local variables, your code will work:
IF ((##error = 0) AND (##rowcount = 1))
But you might rather try try...catch error handling and test ##rowcount separately after update.
UPDATE: doing it in single update:
UPDATE t
SET cat_ord = tt.newCatOrd
FROM Tb_Project_Image t
INNER JOIN #tempTable tt
ON t.id = tt.PI_ID
-- If there was PI_ID not found in Tb_Project_Image
-- But I think that this should have been dealt with
-- During the initial loading of temporary table
IF ##ROWCOUNT <> (select count (*) from #tempTable)
BEGIN
-- Error reporting here
ROLLBACK TRANSACTION
END

Answer 2

Instead of updating and then rolling back, you could also use a CTE to determine if any records should be updated prior to performing the update. Something like this should work:
WITH NON_SINGLETON AS (
-- Find any records in #tempTable that don't match
-- exactly one record in Tb_Project_Image
SELECT t.PI_ID, COUNT(pi.id) C
FROM #tempTable t
LEFT JOIN Tb_Project_Image pi ON t.PI_ID = pi.id
GROUP BY t.PI_ID
HAVING COUNT(pi.id) != 1
)
UPDATE Tb_Project_Image
SET cat_ord = t.newCatOrd
FROM Tb_Project_Image pi
JOIN #tempTable t ON pi.id = t.PI_ID
-- If any invalid records were found in the CTE,
-- then this condition will fail for all rows
-- and nothing will be updated
WHERE NOT EXISTS(SELECT 1 FROM NON_SINGLETON)
If it's possible for #tempTable to have duplicate entries for the same PI_ID, then this will handle those scenarios as well. And since it's a single statement, you don't have to explicitly managing the transaction in the proc (if it's the only thing that needs to be included in the transaction).