CREATE TABLE table_12753 ("Season" FLOAT, "Winners" TEXT, "Total wins" FLOAT, "Runners-up" TEXT, "Third-place" TEXT, "Number of clubs" FLOAT)

What is the sum of the season with 8 clubs and shanghai as the runners-up?
SELECT SUM("Season") FROM table_12753 WHERE "Number of clubs" = '8' AND "Runners-up" = 'shanghai'
SELECT SUM("Season") FROM "table_12753" WHERE "Number of clubs" = '8' AND "Runners-up" = 'shanghai'