WHY "@PIVOT_QUERY" IS NOT GENERATING??

Question

Hi Experts,
I'm trying to use COALESCE function with dynamic SQL.
If I set @PU_ID = 28 OR 29, then results are coming, if if I set @PU_ID = NULL, no result, WHY?
Basically, I'm trying to do below,
1. If my SP receive @PU_ID > 0, then only particular @PU_ID result, or else
2. If my SP receive @PU_ID as NULL, then all @PU_ID result sum together.
Please suggest! Thanks ! and here is sample table, data & query,
CREATE TABLE DBO.TEST_DATA(PU_ID INT NOT NULL, PU_DATE DATE NOT NULL, X_COUNT INT NULL, Y_COUNT INT NULL)
INSERT INTO DBO.TEST_DATA VALUES(28, '2014-01-01', 10, 20), (28, '2014-01-02', 30, 20), (28, '2014-12-12', 10, 20), (28, '2015-02-02', 10, 20)
, (29, '2015-02-02', 10, 20), (29, '2015-02-02', 10, 20)
DECLARE @PIVOT_COLS NVARCHAR(1000), @PIVOT_QUERY NVARCHAR(2000)
DECLARE @PU_ID INT
SET @PU_ID = NULL
--SET @PU_ID = 28
SELECT @PIVOT_COLS = STUFF((SELECT '],[' + REPLACE(RIGHT(CONVERT(VARCHAR(11), PU_DATE,106),8),' ','-')
FROM TEST_DATA GROUP BY REPLACE(RIGHT(CONVERT(VARCHAR(11), PU_DATE,106),8),' ','-')
ORDER BY CAST('01-'+ REPLACE(RIGHT(CONVERT(VARCHAR(11), PU_DATE,106),8),' ','-') AS DATETIME) FOR XML PATH('') ), 1, 2, '') + ']'
--PRINT @PIVOT_COLS
SET @PIVOT_QUERY = N'SELECT *'+ 'FROM ( SELECT * FROM (SELECT CONVERT(CHAR(3), PU_DATE, 0) + ''-'' + CAST(YEAR(PU_DATE) AS VARCHAR) PU_DATE,
SUM(X_COUNT) X_COUNT, SUM(Y_COUNT) Y_COUNT
FROM TEST_DATA WHERE PU_ID = COALESCE(' + CAST(@PU_ID AS VARCHAR) + ', PU_ID)
GROUP BY CONVERT(CHAR(3), PU_DATE, 0) + ''-'' + CAST(YEAR(PU_DATE) AS VARCHAR) ) TMP
UNPIVOT (COL FOR [GROUP] IN (X_COUNT, Y_COUNT) ) AS UNPVT ) PVT ' + 'PIVOT ' + '(MAX(COL) FOR PU_DATE IN (' + @PIVOT_COLS + ')) AS J'
--PRINT @PIVOT_QUERY
EXEC (@PIVOT_QUERY)
DROP TABLE DBO.TEST_DATA

Answer 1

You have:
SET @PU_ID = NULL
--SET @PU_ID = 28
And then:
FROM TEST_DATA WHERE PU_ID = COALESCE(' + CAST(@PU_ID AS VARCHAR) + ', PU_ID)
But since @PU_ID is NULL the result of the entire concatenation is NULL. The fact that you have a coalesce inside the SQL string has nothing to do with it. At the point the query string that is just a bunch of bytes.
Overall, don't inline parameters in your dynamic SQL strings. It comes with all sorts of problems, and this is one of them. Instead use parameterised SQL, which is a lot simpler. The @PIVOT_COLS you need to keep, since column names cannnot be parameterised,
but for all simple parameters, you should use, well, parameters.
CREATE TABLE TEST_DATA(PU_ID INT NOT NULL, PU_DATE DATE NOT NULL, X_COUNT INT NULL, Y_COUNT INT NULL)
INSERT INTO TEST_DATA VALUES(28, '2014-01-01', 10, 20), (28, '2014-01-02', 30, 20), (28, '2014-12-12', 10, 20), (28, '2015-02-02', 10, 20)
, (29, '2015-02-02', 10, 20), (29, '2015-02-02', 10, 20)
DECLARE @PIVOT_COLS NVARCHAR(1000), @PIVOT_QUERY NVARCHAR(2000)
DECLARE @PU_ID INT
SET @PU_ID = NULL
--SET @PU_ID = 28
SELECT @PIVOT_COLS = STUFF((SELECT '],[' + REPLACE(RIGHT(CONVERT(VARCHAR(11), PU_DATE,106),8),' ','-')
FROM TEST_DATA GROUP BY   REPLACE(RIGHT(CONVERT(VARCHAR(11), PU_DATE,106),8),' ','-')
ORDER BY CAST('01-'+ REPLACE(RIGHT(CONVERT(VARCHAR(11), PU_DATE,106),8),' ','-') AS DATETIME) FOR XML PATH('') ), 1, 2, '') + ']'
PRINT @PIVOT_COLS
SET @PIVOT_QUERY = N'SELECT *'+ 'FROM ( SELECT * FROM (SELECT CONVERT(CHAR(3), PU_DATE, 0) + ''-'' + CAST(YEAR(PU_DATE) AS VARCHAR) PU_DATE,
SUM(X_COUNT) X_COUNT, SUM(Y_COUNT) Y_COUNT
FROM TEST_DATA WHERE PU_ID = COALESCE(@PU_ID, PU_ID)
GROUP BY CONVERT(CHAR(3), PU_DATE, 0) + ''-'' + CAST(YEAR(PU_DATE) AS VARCHAR)  ) TMP
UNPIVOT (COL FOR [GROUP] IN (X_COUNT, Y_COUNT) ) AS UNPVT ) PVT ' + 'PIVOT ' + '(MAX(COL) FOR PU_DATE IN (' + @PIVOT_COLS + ')) AS J'
PRINT @PIVOT_QUERY
EXEC sp_executesql @PIVOT_QUERY, N'@PU_ID int', @PU_ID
go
DROP TABLE TEST_DATA
Erland Sommarskog, SQL Server MVP, [email protected]