SQL Server - Using COALESCE across a Pivot with variable columns - sql

Question

I am amending a SQL query that populates a UI table. I want to eliminate any nulls that result from the query and replace them with 0.00. Typically a COALESCE function on the final SELECT would give me what I need, but the columns in the pivot (#ListOfYears) might change (SELECT PV.* may give me 1 column or 10 columns depending on #ListofYears).
DECLARE #ListofYears varchar(6000)
DECLARE #SQL varchar(2000)
SET #ListofYears = '[2021],[2022]'
SET #SQL = '
SELECT PV.*
FROM
(SELECT
p.Pkey,
p.Code,
P.Name as Name,
Price,
GroupName
FROM
Catalogue C
LEFT JOIN CatalogueDetail CD on CD.CataloguePkey=C.Pkey
LEFT JOIN CatalogueYear CY on CY.Pkey=CD.CatalogueYearPkey where C.IsActive=1
) as D
PIVOT
(
COALESCE(Sum(D.Price), 0.00) for GroupName in ( ' + #ListofYears + ' )
) AS PV
ORDER BY Pkey'
PRINT #sql
EXEC (#sql)
Is there any way to use COALESCE or ISNULL so that my top SELECT statement does not result in any NULLS? Putting COALESCE in the pivot results in:
Msg 102, Level 15, State 1, Line 4
Incorrect syntax near ','.
Msg 156, Level 15, State 1, Line 22
Incorrect syntax near the keyword 'COALESCE'.

Answer 1

As I mentioned in the question, you need to wrap the COALESCE in the outer SELECT, not in the PIVOT. This means, in short, you need something like this:
SELECT {Other Columns},
COALESCE([2020],0) AS [2020],
COALESCE([2021],0) AS [2021]
...
FROM(SELECT p.Pkey,
p.Code,
P.Name as Name,
Price,
GroupName
FROM dbo.Catalogue C
LEFT JOIN dbo.CatalogueDetail CD on CD.CataloguePkey=C.Pkey
LEFT JOIN dbo.CatalogueYear CY on CY.Pkey=CD.CatalogueYearPkey
WHERE C.IsActive=1
) as D
PIVOT(SUM(D.Price)
FOR GroupName in ([2021],[2022])) AS PV
ORDER BY Pkey;
As you are using dynamic SQL, and injecting a list into you are, unsurprisingly, finding this difficult.
In truth, I would suggest switching to conditional aggregation, as this is much easier. Non-dynamic it would look like this:
SELECT {Other Columns}
SUM(CASE GroupName WHEN 2020 THEN D.Price ELSE 0 END) AS [2020],
SUM(CASE GroupName WHEN 2021 THEN D.Price ELSE 0 END) AS [2021]
FROM dbo.Catalogue C
LEFT JOIN dbo.CatalogueDetail CD on CD.CataloguePkey=C.Pkey
LEFT JOIN dbo.CatalogueYear CY on CY.Pkey=CD.CatalogueYearPkey
WHERE C.IsActive=1
GROUP BY {Other Columns};
As you want to do this dynamically, it would look a little like this (assuming you are using SQL Server 2017+):
DECLARE #Years table (Year int);
INSERT INTO #Years (Year)
VALUES (2020),(2021);
DECLARE #SQL nvarchar(MAX),
#CRLF nchar(2) = NCHAR(13) + NCHAR(10);
DECLARE #Delim nvarchar(20) = N',' + #CRLF;
SET #SQL = (SELECT N'SELECT {Other Columns}' + #CRLF +
STRING_AGG(N' SUM(CASE GroupName WHEN ' + QUOTENAME(Y.Year,'''') + N'THEN D.Price ELSE 0 END) AS ' + QUOTENAME(Y.Year),#Delim) WITHIN GROUP (ORDER BY Y.Year) + #CRLF +
N'FROM dbo.Catalogue C' + #CRLF +
N' LEFT JOIN dbo.CatalogueDetail CD on CD.CataloguePkey=C.Pkey' + #CRLF +
N' LEFT JOIN dbo.CatalogueYear CY on CY.Pkey=CD.CatalogueYearPkey' + #CRLF +
N'WHERE C.IsActive=1' + #CRLF +
N'GROUP BY {Other Columns};'
FROM #Years Y);
EXEC sys.sp_executesql #SQL;
If you are using a version of SQL Server that isn't fully supported, you'll need to use the "old" FOR XML PATH (and STUFF) method.
Obviously, you'll also need to replace the parts in braces with the appropriate SQL.