在SQL中，可以使用以下技巧來對count去重：
SELECT COUNT(DISTINCT column_name) FROM table_name;
SELECT COUNT(*) FROM (SELECT DISTINCT column_name FROM table_name) AS subquery;
SELECT COUNT(*) FROM (SELECT column_name, ROW_NUMBER() OVER (PARTITION BY column_name) AS rn FROM table_name) AS subquery WHERE rn = 1;
