How to use STRING_AGG to concatenate strings with grouping

Question:  Below is table and expected result. What is the query to achieve this result
Table : Test

ID LOT
7065161 4
7065212 1
7065212 4
7065203 1
7065203 2
7065203 3

Expected Result of query

ID LOT
7065161 4
7065212 1_4
7065203 1_2_3

Answer: Previous to SQL Server 2017 - I use to use the COALESCE function , but since SQL Server 2017 - a new function was introduced : STRING_AGG . According to MS documentation "Concatenates the values of string expressions and places separator values between them. The separator is not added at the end of string"

There is no better way to illustrate STRING_AGG than with an example query.

create table #t1
(ID char(7),LOT char (1))
INSERT INTO #t1
select '7065161','4'
UNION
select '7065212', '1'
UNION
select '7065212','4'
UNION
select '7065203','1'
UNION
select '7065203', '2'
UNION
select '7065203', '3'

SELECT ID, STRING_AGG(LOT, '_') as LOT
FROM #t1
GROUP BY ID;


drop table #t1

--------RESULTS----------
ID	LOT
7065161	4
7065203	1_2_3
7065212	1_4

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