Looking for missing gaps for getting "Only one expression can be specified in the select list when the subquery is not introduced with EXISTS." - sql

Question

I have the following query to find missing gaps in the sort for each ModelID but I keep getting the following error and don't know why.
What I'm doing is in my first loop I am looping through the modelID's and in the inner loop I am looking for the missing gaps in the siSort column for that modelID and putting that into a temp table.
Msg 116, Level 16, State 1, Line 27
Only one expression can be specified in the select list when the subquery is not introduced with EXISTS.
USE crm
GO
BEGIN
DECLARE #ID INT
DECLARE #MAXID INT
DECLARE #COUNT INT
DECLARE #iCustomListModelID INT
DECLARE #iCustomFieldID INT
DECLARE #MissingIds TABLE (ID INT)
DECLARE #Output TABLE (iCustomListModelID INT, siSort INT, iListItemID INT)
-- SELECT ALL DISTINCT ICustomListModelID's FROM CustomList Table
SELECT DISTINCT cl.iCustomListModelID
INTO #DistinctModelIDs
FROM dbo.CustomListModel clm
INNER JOIN dbo.CustomListType clt ON clm.iCustomListTypeID = clt.iCustomListTypeID
AND clt.vchCustomListTypeDescription = N'Household Custom Field'
INNER JOIN dbo.CustomList cl ON clm.iCustomListModelID = cl.iCustomListModelID
INNER JOIN dbo.CustomField cf ON cl.iListItemID = cf.iCustomFieldID
ORDER BY cl.iCustomListModelID
-- Get iCustomFieldID to insert into iListItemID
SET #iCustomFieldID = (SELECT * FROM dbo.CustomField cf WHERE vchLabel = '')
-- Begin Outer loop to go through each iCustomListModelID
WHILE (SELECT COUNT(iCustomListModelID) AS Total FROM #DistinctModelIDs) > 0
BEGIN
-- GRAB THE NEXT iCustomListModelID
SELECT #iCustomListModelID = (SELECT TOP 1 iCustomListModelID FROM #DistinctModelIDs);
DROP TABLE #List
SELECT siSort INTO #List FROM CustomList WHERE iCustomListModelID = #iCustomListModelID
SELECT #MAXID = siSort FROM dbo.CustomList WHERE iCustomListModelID = #iCustomListModelID
SET #ID = 1;
-- Inner loop to go through the missing gaps in siSort
WHILE #ID <= #MAXID
BEGIN
IF NOT EXISTS (
SELECT 'X' FROM #List WHERE siSort = #ID
)
INSERT INTO #MissingIDs (ID)
VALUES (#ID)
--INSERT THE MISSING ID INTO #outputTable Table
INSERT INTO #Output (iCustomListModelID, siSort, iListItemID)
VALUES (#iCustomListModelID, #ID, #iCustomFieldID)
SET #ID = #ID + 1;
END;
-- DELETE CURRENT iCustomListModelID
DELETE FROM #DistinctModelIDs WHERE iCustomListModelID = #iCustomListModelID
END
SELECT * FROM #Output
END;

Answer 1

One possibility is that the issue is this line:
SET #iCustomFieldID = (SELECT * FROM dbo.CustomField cf WHERE vchLabel = '')
If dbo.CustomerField doesn't have exactly one column (more than one column seems likely because vchLabel is already one column in the table), then this will generate an error of that type.