What is the number of commanders that had 0 off 63 men killed?
CREATE TABLE "table1_2596811_12" (
  "unit" text,
  "commander" text,
  "complement" text,
  "killed" text,
  "wounded" text,
  "missing" text
);
SELECT COUNT("commander") FROM "table1_2596811_12" WHERE "killed"='0 off 63 men';