Sour is known as a alcoholic drink containing base liquor, lime or lemon juice and sweetener outside of Japan but Japanese sour, especially offered in Izakaya type restaurants are different. Japanese sour contains shochu as base alcohol and other beverage, sweetner or fruits. If the sour does not contain other beverage such as oolong tea or green tea, the sour contains soda.
Typical Japanese sours are Lemon sour and Grapefruit sour. These sours contain the fruits(+its juice), shochu and soda.
Japanese sour is sometimes called as Chuhai(or shorten as Hai). Sour containing oolong tea is not called Oolong sour but Oolong hai. Then, Oolong hai does not contain soda. Therefore shochu base mixed drink containing soda is Sour but without soda is called hai.