CREATE TABLE table_797 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

When was incumbent John N. Tillman first elected?
SELECT MIN("First elected") FROM table_797 WHERE "Incumbent" = 'John N. Tillman'
SELECT MIN("First elected") FROM "table_797" WHERE "Incumbent" = 'John N. Tillman'