CREATE TABLE table_1555308_1 (prothrombin_time VARCHAR2, platelet_count VARCHAR2)

How many entries for prothrombin time are there where platelet count is 'decreased or unaffected'?
SELECT COUNT(prothrombin_time) FROM table_1555308_1 WHERE platelet_count = "Decreased or unaffected"
SELECT COUNT("prothrombin_time") FROM "table_1555308_1" WHERE "Decreased or unaffected" = "platelet_count"