SQL Server; How to incorporate unique values from STRING_AGG? - sql

Question

There are a handful of discussions on how to setup unique values with respect to STRING_AGG, see:
https://stackoverflow.com/a/51646573/6534818
https://stackoverflow.com/a/50589222/6534818
but I am struggling to port them over to my case as I would like to maintain my ordering of results as well as management of NULL.
Consider the following MWE -- how might I just return the distinct/unique values for the STRING_AGG operation?
CREATE TABLE #bridge (dim2Key int, groupKey int)
INSERT #bridge (dim2Key, groupKey)
VALUES (1, 1)
,(2, 1)
,(3, 1)
,(4, 2)
,(5, NULL)
CREATE TABLE #dim2 (dim2Key int, attributeOne varchar(255))
INSERT #dim2 (dim2Key, attributeOne)
VALUES (1, 'B')
,(2, 'A')
,(3, 'A')
,(4, NULL)
CREATE TABLE #dim1 (dim1Key int, attributeTwo int, attributeThree varchar(255))
INSERT #dim1 (dim1Key, attributeTwo, attributeThree)
VALUES (1, 35, 'val1')
,(2, 25, 'val2')
,(3, 45, 'val3')
,(4, 55, 'val1')
,(5, NULL, NULL)
CREATE TABLE #fact1 (dim1Key int, factvalue1 int, groupKey int)
INSERT #fact1 (dim1Key, factvalue1, groupKey)
VALUES (1, 5, 1)
,(2, 25, 1)
,(3, 55, 1)
,(4, 99, 2)
,(5, 99, NULL)
GO
SELECT
#fact1.dim1Key,
#fact1.factvalue1,
#fact1.groupKey,
#dim1.attributeTwo,
#dim1.attributeThree,
ISNULL(#dim2.attributeOne, '<missing>')
FROM #fact1
JOIN #dim1 ON #dim1.dim1key = #fact1.dim1key
CROSS APPLY (
SELECT attributeOne = STRING_AGG(ISNULL(#dim2.attributeOne, '<missing>'), ', ') WITHIN GROUP (ORDER BY #dim2.attributeOne)
FROM #bridge b
JOIN #dim2 ON #dim2.dim2key = b.dim2key
WHERE b.groupKey = #fact1.groupKey
) #dim2

Answer 1

Just put it in a subquery with DISTINCT
SELECT
#fact1.dim1Key,
#fact1.factvalue1,
#fact1.groupKey,
#dim1.attributeTwo,
#dim1.attributeThree,
ISNULL(#dim2.attributeOne, '<missing>')
FROM #fact1
JOIN #dim1 ON #dim1.dim1key = #fact1.dim1key
CROSS APPLY (
SELECT
attributeOne = STRING_AGG(ISNULL(d2.attributeOne, '<missing>'), ', ') WITHIN GROUP (ORDER BY d2.attributeOne)
FROM (
SELECT DISTINCT
#dim2.attributeOne
FROM #bridge b
JOIN #dim2 ON #dim2.dim2key = b.dim2key
WHERE b.groupKey = #fact1.groupKey
) d2
) #dim2