SQL with Manoj

 
In one of my [previous post] I discussed about a new function STRING_SPLIT() introduced in SQL Server 2016, which splits a Sentence or CSV String to multiple values or rows.
 

Now with the latest CTP 1.x version of SQL Server vNext (I’m calling it “SQL Server 2017”) a new function is introduced to just do its reverse, i.e. Concatenate string values or expressions separated by any character.

The STRING_AGG() aggregate function takes all expressions from rows and concatenates them into a single string in a single row.

It implicitly converts all expressions to String type and then concatenates with the separator defined.
 

–> In the example below I’ll populate a table with States and Cities in separate rows, and then try to Concatenate Cities belonging to same States:

USE tempdb
GO

CREATE TABLE #tempCityState (
    [State] VARCHAR(5), 
    [Cities] VARCHAR(50)
)
GO

INSERT INTO #tempCityState

SELECT 'CA', 'Hanford'
UNION ALL
SELECT 'CA', 'Fremont'
UNION ALL
SELECT 'CA', 'Los Anggeles'
UNION ALL
SELECT 'CO', 'Denver'
UNION ALL
SELECT 'CO', 'Aspen'
UNION ALL
SELECT 'CO', 'Vail'
UNION ALL
SELECT 'CO', 'Teluride'
UNION ALL
SELECT 'WA', 'Seattle'
UNION ALL
SELECT 'WA', 'Redmond'
UNION ALL
SELECT 'WA', 'Bellvue'
GO

SELECT * FROM #tempCityState

State	Cities
CA	Hanford
CA	Fremont
CA	Los Anggeles
CO	Denver
CO	Aspen
CO	Vail
CO	Teluride
WA	Seattle
WA	Redmond
WA	Bellvue

–> To comma separate values under a single row you just need to apply the STRING_AGG() function:

SELECT 
	STRING_AGG(Cities, ', ') as AllCities
FROM #tempCityState

-- Use "WITHIN GROUP (ORDER BY ...)" clause to concatenate them in an Order:
SELECT 
	STRING_AGG(Cities, ', ') WITHIN GROUP (ORDER BY Cities) as AllCitiesSorted
FROM #tempCityState

–> Now to Concatenate them by States, you just need to group them by the State, like any other aggregate function:

SELECT 
	State, 
	STRING_AGG(Cities, ', ') as CitiesByStates
FROM #tempCityState
GROUP BY State

-- Use "WITHIN GROUP (ORDER BY ...)" clause to concatenate them in an Order:
	State, 
	STRING_AGG(Cities, ', ') WITHIN GROUP (ORDER BY Cities) as CitiesByStatesSorted
FROM #tempCityState
GROUP BY State

You can check more about STRING_AGG() on MSDN.