CREATE TABLE "round_1" (
  "rank" real,
  "heat" real,
  "name" text,
  "nationality" text,
  "result" text
);

Question: What is Melaine Walker's Rank?
SQL: SELECT SUM("rank") FROM "round_1" WHERE "name"='melaine walker';

Question: What is the Name of the Player with a Rank of 23 or less, Heat of 4 and Result of 55.91?
SQL: SELECT "name" FROM "round_1" WHERE "heat"=4 AND "rank"<23 AND "result"='55.91';

Question: What is the Heat of the Player with a Rank of 18 or less and Result of 55.15?
SQL: SELECT "heat" FROM "round_1" WHERE "rank"<18 AND "result"='55.15';