Strip the last dynamic column from ending comma? - sql

Question

I am writing the following dynamic SQL, and getting an error around the FROM keyword.
Incorrect syntax near the keyword 'FROM'.
' + #columnList + '
FROM [History]
I know why, its because there shouldn't be a comma that precedes it. However, since the column before it (#columnList) is a result of dynamic SQL, how do I go about resolving this?
Basically, I need a way to make
SELECT #columnList =....
not append a comma at the end to the LAST column/Account selected.
The comma is added at the end at this part:
quotename(AccTbl.Account), ',',
Full Query:
DECLARE #sqlCommand NVARCHAR(MAX) = '',
#columnList NVARCHAR(MAX) = '',
#pivotColumns NVARCHAR(MAX) = '';
SELECT #columnList =
(SELECT DISTINCT concat(CHAR(9), 'COALESCE(', quotename(AccTbl.Account), ', 0)', quotename(AccTbl.Account), ',', CHAR(10)) --CHAR(9) & CHAR(10) for indentation/formatting
FROM [Accounts] AccTbl
WHERE AccTbl.Account NOT IN ('WS')
FOR XML Path(''), TYPE).value('(./text())[1]', 'NVARCHAR(MAX)');
SELECT #pivotColumns = STUFF(
(SELECT DISTINCT concat(CHAR(9), ',', quotename(AccTbl.Account), CHAR(10))
FROM [Accounts] AccTbl
WHERE AccTbl.Account NOT IN ('WS')
FOR XML Path(''), TYPE).value('(./text())[1]', 'NVARCHAR(MAX)'), 1, 1, '');
/*
EXEC the sqlCommand as separate batches to prevent this error: 'CREATE VIEW' must be the first statement in a query batch.
https://stackoverflow.com/a/39135516/8397835
*/
SET #sqlCommand = '
USE [ABC_DB]
--GO
DROP VIEW IF EXISTS [dbo].[Piv];
--GO
SET ANSI_NULLS ON
--GO
SET QUOTED_IDENTIFIER ON
--GO
';
Execute sp_executesql #sqlCommand;
SET #sqlCommand = '
CREATE VIEW [dbo].[Piv]
AS
(SELECT
[Style Code],
' + #columnList + '
FROM [History]
PIVOT (SUM([Value]) FOR [Accounts] IN (
' + #pivotColumns + '
)
)
AS Piv);
';
PRINT #sqlCommand;
Execute sp_executesql #sqlCommand;
In other words, whats happening right now is something like this:
UPDATE:
#columnList was fixed with leading comma instead of trailing comma, but leading comma nor trailing comma would work for #pivotColumns because we don't have a pre-existing column in the PIVOT part of the query like we do in the SELECT statement with Style Code.

Answer 1

Don't put the commas at the end, put them at the start, and then strip the first character, using STUFF, that's far easier in T-SQL.
So instead of {Expression} + ',' do ',' + {Expression}. Then you can simply do STUFF(#columnList,1,1,'') to remove the leading comma instead.

Answer 2

Part of the problem is your 'formatting' of the code. Generally I would agree that formatting the dynamic code can help in debugging - here it is getting in the way.
SELECT #columnList = STUFF(
(SELECT DISTINCT concat(', ', quotename(AccTbl.Account))
FROM [Accounts] AccTbl
WHERE AccTbl.Account NOT IN ('WS')
FOR XML Path(''), TYPE).value('(./text())[1]', 'NVARCHAR(MAX)'), 1, 1, '');
SELECT #pivotColumns = STUFF(
(SELECT DISTINCT concat(', ', quotename(AccTbl.Account))
FROM [Accounts] AccTbl
WHERE AccTbl.Account NOT IN ('WS')
FOR XML Path(''), TYPE).value('(./text())[1]', 'NVARCHAR(MAX)'), 1, 1, '');
Removing those - we see that both statements are exactly the same. Assume the results from the Accounts table are: Acct1, Acct2
You would get the result as '[Acct1], [Acct2]' for both #columnList and #pivotColumns. So - if you want to expand on the column list portion, for example add the table alias (which is what I would do):
SELECT #columnList = STUFF(
(SELECT DISTINCT concat(', ', 'h.', quotename(AccTbl.Account))
FROM [Accounts] AccTbl
WHERE AccTbl.Account NOT IN ('WS')
FOR XML Path(''), TYPE).value('(./text())[1]', 'NVARCHAR(MAX)'), 1, 1, '');
I would not bother with formatting these columns in the final result, since you will be recreating the view as needed using dynamic SQL.
SET #sqlCommand = '
CREATE VIEW [dbo].[Piv]
AS
(SELECT
h.[Style Code],
' + #columnList + '
FROM [History] h
PIVOT (SUM(h.[Value]) FOR [Accounts] IN (
' + #pivotColumns + '
)
)
AS Piv);
';