CREATE TABLE table_715 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

What is the minimum first elected for ed markey?
SELECT MIN("First elected") FROM table_715 WHERE "Incumbent" = 'Ed Markey'
SELECT MIN("First elected") FROM "table_715" WHERE "Incumbent" = 'Ed Markey'