Using IF without an ELSE condition in SQL - sql

Question

I'm trying to use the below query to update some data only if #rowcount is greater than 0. However, its executing the update statement even when #RowCount is 0. Can someone help whats wrong in here please? I would like to do nothing if #RowCount is 0.
I'm using SQL Server 2014.
TRUNCATE TABLE Count1
DECLARE #RowCount AS INT
--insert data in a temporary table
SELECT YEAR, S_ID
into #Count1 FROM
(SELECT DISTINCT D.YEAR, S_ID FROM SALES S JOIN TRANSACTIONS PT
ON S.COMBINED_TXN_ID = PT.S_ID AND PT.TRANSACTION_TYPE = 'BILLING'
JOIN DATE D ON D.DAY = S.DAY AND PT.DAY = S.DAY
WHERE
S.SALES_CUSTOMER != PT.CUSTOMER)Counter1;
--Store the rowcount in a temporary variable
SET #RowCount = (SELECT Count(*) FROM #Count1)
--Fix the data with differences only if count>0
IF ##ROWCOUNT > 0
BEGIN
UPDATE SALES
SET SALES_CUSTOMER = PT.CUSTOMER
FROM SALES S
JOIN TRANSACTIONS PT ON S.COMBINED_TXN_ID = PT.S_ID
JOIN DATE D ON D.DAY = S.DAY AND PT.DAY = S.DAY
WHERE
S_ID IN (SELECT S_ID FROM #Count1)
END;

Answer 1

##ROWCOUNT Returns the number of rows affected by the last statement.
Change system variable ##ROWCOUNT by your own variable #RowCount
--Store the rowcount in a temporary variable
SET #RowCount = (SELECT Count(*) FROM #Count1)
--Fix the data with differences only if count>0
IF #RowCount > 0

Answer 2

You are confusing the local variable #RowCount you defined yourself, with the global variable ##ROWCOUNT Microsoft defined for you (which you can't set).
So simply refer to the correct variable. Better yet: rename your local variable to avoid such confusion.
You don't even need the if at all, since the update wouldn't be executed if #Count1 is empty as there are no records to fulfill the where clause (WHERE S_ID IN ({empty result set})).

Answer 3

If you wish to use the same variable you have declared use #rowcount
DECLARE #recordCount INT
--insert data in a temporary table
SELECT YEAR
,S_ID
INTO #Count1
FROM (
SELECT DISTINCT D.YEAR
,S_ID
FROM SALES S
INNER JOIN TRANSACTIONS PT
ON S.COMBINED_TXN_ID = PT.S_ID
AND PT.TRANSACTION_TYPE = 'BILLING'
INNER JOIN DATE D
ON D.DAY = S.DAY
AND PT.DAY = S.DAY
WHERE S.SALES_CUSTOMER != PT.CUSTOMER
) Counter1;
--Store the rowcount in a temporary variable
SELECT #recordCount = count(*)
FROM #Count1
--Fix the data with differences only if count>0
IF (#recordCount > 0)
BEGIN
UPDATE SALES
SET SALES_CUSTOMER = PT.CUSTOMER
FROM SALES S
INNER JOIN TRANSACTIONS PT
ON S.COMBINED_TXN_ID = PT.S_ID
INNER JOIN DATE D
ON D.DAY = S.DAY
AND PT.DAY = S.DAY
WHERE S_ID IN (
SELECT S_ID
FROM #Count1
)
END

Answer 4

You could skip all the temp tables and checks and just do an update. Something like this should be the same thing as all the code you posted.
UPDATE S
SET SALES_CUSTOMER = PT.CUSTOMER
FROM SALES S
JOIN S PT ON S.COMBINED_TXN_ID = PT.S_ID
AND PT.TRANSACTION_TYPE = 'BILLING'
JOIN DATE D ON D.DAY = S.DAY
AND PT.DAY = S.DAY
WHERE S.SALES_CUSTOMER != PT.CUSTOMER