location

t1.username = t2.username AND t2.type != 3 AND t2.Location != null AND
 (t2.DateTime between t1.Datetime +15 min AND t1.Datetime -15)

UserName, Type, Location

SELECT
    id,
    username,
    type,
    COALESCE(location,
        CASE
            (SELECT id FROM table1 INNER JOIN table2 ON t1.username = t2.username WHERE t2.type != 3 AND t2.Location != null AND
                (t2.DateTime between t1.Datetime +15 min AND t1.Datetime -15))
        END) AS location,
    datetime
FROM table_name