How to sort the result from string_agg()

For Microsoft SQL: Use "WITHIN GROUP"

https://docs.microsoft.com/en-us/sql/t-sql/functions/string-agg-transact-sql?view=sql-server-2017

SELECT
  STRING_AGG(prod, '|') WITHIN GROUP (ORDER BY product)
FROM ...

select string_agg(prod,' | ') FROM 
  (SELECT product as prod FROM tblproducts ORDER BY product )MAIN;

SQL FIDDLE

With postgres 9.0+ you can write:

select string_agg(product,' | ' order by product) from "tblproducts"

Details here.

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