Generating Unique Values with SQL Server 2017's STRING_AGG Function
The STRING_AGG
function in SQL Server 2017 doesn't directly support distinct values. However, achieving unique aggregated results is possible using a two-step approach. This method avoids the invalid syntax of STRING_AGG(DISTINCT column, ',')
.
The solution involves a Common Table Expression (CTE) to pre-process the data. The CTE groups the data to eliminate duplicates before the final aggregation.
The example below demonstrates this technique. The initial Sitings
CTE provides sample data. The CTE_Animals
CTE then groups by State
, City
, and Siting
to remove redundant entries. The main query then uses STRING_AGG
to concatenate the unique Siting
values for each State
and City
combination.
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(*) AS [# Of Sitings], STRING_AGG(Siting,',') AS Animals FROM CTE_Animals GROUP BY State, City ORDER BY State, City;
This approach guarantees that the final Animals
column contains only unique animal sightings for each location, while the # Of Sitings
column reflects the distinct count. The ORDER BY
clause ensures a consistent and predictable output order.
The above is the detailed content of How Can I Get Distinct Results Using STRING_AGG in SQL Server 2017?. For more information, please follow other related articles on the PHP Chinese website!

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