Produce DISTINCT values in STRING_AGG

Question

I'm using the STRING_AGG function in SQL Server 2017. I'd like to create the same effect as COUNT(DISTINCT <column>). I tried STRING_AGG(DISTINCT <column>,',') but that is not legal syntax.

I'd like to know if there is a T-SQL work-around. Here is my sample:

WITH Sitings    AS   (     SELECT * FROM (VALUES        (1, 'Florida', 'Orlando', 'bird'),       (2, 'Florida', 'Orlando', 'dog'),       (3, 'Arizona', 'Phoenix', 'bird'),       (4, 'Arizona', 'Phoenix', 'dog'),       (5, 'Arizona', 'Phoenix', 'bird'),       (6, 'Arizona', 'Phoenix', 'bird'),       (7, 'Arizona', 'Phoenix', 'bird'),       (8, 'Arizona', 'Flagstaff', 'dog')     ) F (ID, State, City, Siting)   )  SELECT State, City, COUNT(DISTINCT Siting) [# Of Types], STRING_AGG(Siting,',') Animals FROM Sitings  GROUP BY State, City 

The above produces the following result:

+---------+-----------+--------------+-------------------------+ |  State  |   City    | # Of Types   |         Animals         | +---------+-----------+--------------+-------------------------+ | Arizona | Flagstaff |            1 | dog                     | | Florida | Orlando   |            2 | dog,bird                | | Arizona | Phoenix   |            2 | bird,bird,bird,dog,bird | +---------+-----------+--------------+-------------------------+ 

The output is exactly what I want, except I want the concatenated "Animals" listed for Phoenix Arizona to be DISTINCT, like this:

+---------+-----------+--------------+--------------------+ |  State  |   City    | # Of Types   |      Animals       | +---------+-----------+--------------+--------------------+ | Arizona | Flagstaff |            1 | dog                | | Florida | Orlando   |            2 | dog,bird           | | Arizona | Phoenix   |            2 | bird,dog           | +---------+-----------+--------------+--------------------+ 

Any ideas?

When I use my real data set, which is much larger, I get an error about the "Animals" column exceeding 8000 characters.

My question I think is the same as this one, except my example is much simpler.

Answer 1

Here is one way to do it.

Since you want the distinct counts as well, it can be done simply by grouping the rows twice. The first GROUP BY will remove duplicates, the second GROUP BY will produce the final result.

WITH Sitings AS (     SELECT * FROM (VALUES      (1, 'Florida', 'Orlando', 'bird'),     (2, 'Florida', 'Orlando', 'dog'),     (3, 'Arizona', 'Phoenix', 'bird'),     (4, 'Arizona', 'Phoenix', 'dog'),     (5, 'Arizona', 'Phoenix', 'bird'),     (6, 'Arizona', 'Phoenix', 'bird'),     (7, 'Arizona', 'Phoenix', 'bird'),     (8, 'Arizona', 'Flagstaff', 'dog')     ) F (ID, State, City, Siting) ) ,CTE_Animals AS (     SELECT         State, City, Siting     FROM Sitings     GROUP BY State, City, Siting ) SELECT     State, City, COUNT(1) AS [# Of Sitings], STRING_AGG(Siting,',') AS Animals FROM CTE_Animals GROUP BY State, City ORDER BY     State     ,City ; 

Result

+---------+-----------+--------------+----------+ |  State  |   City    | # Of Sitings | Animals  | +---------+-----------+--------------+----------+ | Arizona | Flagstaff |            1 | dog      | | Arizona | Phoenix   |            2 | bird,dog | | Florida | Orlando   |            2 | bird,dog | +---------+-----------+--------------+----------+ 

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If you are still getting an error message about exceeding 8000 characters, then cast the values to varchar(max) before STRING_AGG.

Something like

STRING_AGG(CAST(Siting AS varchar(max)),',') AS Animals