CREATE TABLE table_51408 ("Year" FLOAT, "Film" CLOB, "Role" CLOB, "Leading Man" CLOB, "Director" CLOB)

What year was the role nan taylor, alias of nan ellis, aka mrs. andrews and directed by William keighley?
SELECT SUM("Year") FROM table_51408 WHERE "Role" = 'nan taylor, alias of nan ellis, aka mrs. andrews' AND "Director" = 'william keighley'
SELECT SUM("Year") FROM "table_51408" WHERE "Director" = 'william keighley' AND "Role" = 'nan taylor, alias of nan ellis, aka mrs. andrews'