循环遍历表中的每个值并将该值作为参数提供给函数

Question

I need to loop through each value in #TempTable and use that value as a parameter for MyFunction

Function MyFunction simply returns another column based on ID_col in #TempTable

IF OBJECT_ID('tempdb..#TempTable') IS NOT NULL DROP TABLE #TempTable
select 'ID1' as ID_col
into #TempTable
union select all 'ID2'
union select all 'ID3'

DECLARE @PriorID_col varchar(50)
DECLARE @ReturnVal varchar(50) = ''

SELECT TOP 1 PriorID_col = #TempTable.ID_col

-- here I need to loop through each ID_col in #TempTable and supply it as a parameter to "MyFunction"
WHILE MyFunction(#TempTable.ID_col) IS NOT NULL 
 BEGIN
        SET @PriorID_col = MyFunction(@PriorID_col)
    END
-- querying ID from real table based on variable @PriorID_col
SELECT TOP 1 @ReturnVal = ID
FROM         MyTable
WHERE        MyTable.ID = @PriorID_col

But I am unable to loop through each value in a #TempTable . What am I doing wrong here?

Answer 1

I don't think your logic quite works, and your union all certainly doesn't. You are getting a value for each row in the temp table, but only using one of those values to obtain the return value, and there doesn't appear to be any relationship between them.

Anyway I have shown the basic premise for iterating through the rows in a temp table. Essentially...

1. Get the top row
2. Do something with it
3. Delete it

IF OBJECT_ID('tempdb..#TempTable') IS NOT NULL DROP TABLE #TempTable;

SELECT 'ID1' AS ID_col
INTO #TempTable
UNION ALL SELECT 'ID2'
UNION ALL SELECT 'ID3';

DECLARE @ID_col VARCHAR(50), @PriorID_col VARCHAR(50), @ReturnVal VARCHAR(50) = '';

-- here I need to loop through each ID_col in #TempTable and supply it as a parameter to "MyFunction"
WHILE EXISTS (SELECT 1 FROM #TempTable.ID_col)
BEGIN
    SELECT TOP 1 @ID_col = ID_col #TempTable.ID_col;
    SET @PriorID_col = dbo.MyFunction(@ID_col)
    DELETE FROM #TempTable.ID_col WHERE ID_col = @ID_col
END;

-- querying ID from real table based on variable @PriorID_col
SELECT TOP 1 @ReturnVal = ID
FROM MyTable
WHERE MyTable.ID = @PriorID_col;

Answer 2

Just wondering, wouldn't simple SELECT ... WHERE work for this scenario.

SELECT 'ID1' AS ID_col
INTO #TempTable
UNION ALL SELECT 'ID2'
UNION ALL SELECT 'ID3';

SELECT *
FROM MyTable
WHERE MyTable.Id IN (SELECT MyFunction(@ID_col) FROM #TempTable)