CREATE TABLE table_18656 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

What district has Riley Joseph Wilson as the incumbent?
SELECT "District" FROM table_18656 WHERE "Incumbent" = 'Riley Joseph Wilson'
SELECT "District" FROM "table_18656" WHERE "Incumbent" = 'Riley Joseph Wilson'