MySQL单表500W条数据统计查询，求个高性能方法

Question

有一张表,500W条记录，4个字段如下：

id int primary keyip intclass_a varcharclass_b varchar

需要执行的查询语句结果是：

SELECT class_a,class_b,count(DISTINCT ip) FROM table GROUP BY class_a, class_b

目前按照上述语句执行，性能几乎为零。求大神给点优化意见。

ip, class_a, class_b 都加过索引了。

Answer 1

u could add commonly index ,eg: "alert table dbname.table add index (classa, classb)", and you can use explain to synatx.