CREATE TABLE table_27833186_1 (rider_names VARCHAR2, horse_name VARCHAR2)

How many different riders are there that won riding Omr Tsunami?
SELECT COUNT(rider_names) FROM table_27833186_1 WHERE horse_name = "OMR Tsunami"
SELECT COUNT("rider_names") FROM "table_27833186_1" WHERE "OMR Tsunami" = "horse_name"