为什么 SELECT COUNT(*) 比 MySQL 中带有 WHERE 子句的 SELECT 慢得多? [英]Why SELECT COUNT(*) is much slower than SELECT with a WHERE clause in MySQL?
为什么我的`sql_calc_found_rows`比MySQL中的`count(*)`要快? [英]Why is my `sql_calc_found_rows` faster than `count(*)` in MySQL?