Port STRING_AGG to FOR XML - sql-server

Question

I'm currently working on Data Discovery and Classification and I have a query that allows me to see a preview of the data while doing the classification.
This is an example of how it works against AdventureWorks:
DECLARE #TableName VARCHAR(100) = 'Product'
DROP TABLE IF EXISTS #ColumnsToDisplay
SELECT ROW_NUMBER () OVER (ORDER BY tab.name) AS Iteration,
SCHEMA_NAME (tab.schema_id) AS schema_name,
tab.name AS table_name,
--col.column_id,
col.name AS column_name,
--t.name AS data_type,
--col.max_length,
--col.precision,
CAST(NULL AS VARCHAR(MAX)) AS DataSample
INTO #ColumnsToDisplay
FROM sys.tables AS tab
JOIN sys.columns AS col
ON col.object_id = tab.object_id
--LEFT JOIN sys.types AS t
-- ON col.user_type_id = t.user_type_id
WHERE tab.name = #TableName
DECLARE #Iterations INT = 0,
#CurrentIteration INT = 1;
SELECT #Iterations = MAX (Iteration)
FROM #ColumnsToDisplay
WHILE #CurrentIteration <= #Iterations
BEGIN
DECLARE #CurrentTableName VARCHAR(100) = '',
#CurrentColumnName VARCHAR(100) = '',
#DynamicQuery NVARCHAR(1000) = N''
DECLARE #Sample VARCHAR(MAX)
SET #CurrentTableName = '';
SET #DynamicQuery = N'';
SELECT #CurrentTableName = CONCAT (ttq.schema_name, '.', ttq.table_name),
#CurrentColumnName = ttq.column_name
FROM #ColumnsToDisplay AS ttq
WHERE ttq.Iteration = #CurrentIteration
IF (#CurrentTableName = '')
BEGIN
SET #CurrentIteration += 1
CONTINUE
END
SET #DynamicQuery = CONCAT (N'
SELECT #Sample = STRING_AGG(t.ColumnData,'', '')
FROM (
SELECT TOP 5 CAST(x.', #CurrentColumnName, ' AS VARCHAR(MAX)) AS ColumnData
FROM ', #CurrentTableName, ' AS x
WHERE x.', #CurrentColumnName, ' IS NOT NULL
)t')
EXECUTE sys.sp_executesql #DynamicQuery,
N'#Sample VARCHAR(MAX) OUTPUT',
#Sample = #Sample OUTPUT
UPDATE #ColumnsToDisplay
SET DataSample = #Sample
WHERE Iteration = #CurrentIteration
SET #CurrentIteration += 1
END
SELECT ctd.Iteration,
ctd.schema_name,
ctd.table_name,
--ctd.column_id,
ctd.column_name,
--ctd.data_type,
--ctd.max_length,
--ctd.precision,
ctd.DataSample
FROM #ColumnsToDisplay AS ctd
Here the result:
Iteration
schema_name
table_name
column_name
DataSample
1
Production
Product
ProductID
980, 365, 771, 404, 977
2
Production
Product
Name
Adjustable Race, All-Purpose Bike Stand, AWC Logo Cap, BB Ball Bearing, Bearing Ball
3
Production
Product
ProductNumber
AR-5381, BA-8327, BB-7421, BB-8107, BB-9108
4
Production
Product
MakeFlag
0, 0, 1, 0, 1
5
Production
Product
FinishedGoodsFlag
0, 0, 0, 0, 0
6
Production
Product
Color
Black, Black, Black, Silver, Silver
The problem is that this query only works from SQL Server 2017 and above because it uses STRING_AGG. For SQL Server 2016 and below I'm supposed to use STUFF instead.
I followed this example but I couldn't really fix it.
The only thing I know is that the part of the code that I need to port is this:
SET #DynamicQuery = CONCAT (N'
SELECT #Sample = STRING_AGG(t.ColumnData,'', '')
FROM (
SELECT TOP 5 CAST(x.', #CurrentColumnName, ' AS VARCHAR(MAX)) AS ColumnData
FROM ', #CurrentTableName, ' AS x
WHERE x.', #CurrentColumnName, ' IS NOT NULL
)t')
Can anyone help me port STRING_AGG to STUFF?
Thank you

Answer 1

First, let's clarify that stuff is, as Stu mentions, just used to remove the first delimiter.
So, if you had
'a','b','c'
and you wanted to use a commas delimiter, xml path would give you:
,a,b,c
and you use stuff to cut off the first comma:
a,b,c
Your query seems to have no delimiters at all, so you won't use stuff. With that out of the picture, here's me untested guess, it's tricky what with the dynamic query added on top of it:
SET #DynamicQuery = CONCAT (N'
set #Sample =
(
select t.ColumnData
from ', #CurrentTableName, ' AS x
where x.', #CurrentColumnName, ' IS NOT NULL
for xml path(''''), type
).value(''.'',''nvarchar(max)'')
)t')

Answer 2

Than you for your help.
The right question was:
SET #DynamicQuery = CONCAT (N'
SELECT #Sample = STUFF((SELECT '', ''+ t.ColumnData
FROM (
SELECT TOP 5 CAST(x.[', #CurrentColumnName, '] AS VARCHAR(MAX)) AS ColumnData
FROM ', #CurrentTableName, ' AS x
WHERE x.[', #CurrentColumnName, '] IS NOT NULL
) AS t
FOR XML PATH('''')),1,1,'''')')