CREATE TABLE table_18323 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

When was the first elected for district missouri 7?
SELECT MIN("First elected") FROM table_18323 WHERE "District" = 'Missouri 7'
SELECT MIN("First elected") FROM "table_18323" WHERE "District" = 'Missouri 7'