There are not many night grocery stores in Riga, where it is possible to buy some food. But there is a night market in Riga, where vegetables and fruits are sold all night long. The farmer’s market is located on the territory of Riga Central Market, on Gaiziņa and Spīķeru Streets. The market is open every day, from 17:00 to 8:00. The produce is sold here in big quantities, however, from 17:00 to 22:00 it also operates as a retail business and everyone can buy the food here in small quantities.
Riga Night Market

I wasn’t aware that there were a night markecan you post the location in the original article, it will be helpful
It starts from Spīķeru iela, 6. There is an address in the article too.