mysql数据库sql语句优化，求大神！！！！

Question

SELECT DISTINCT uid, level,username,ansnum FROM test WHERE level=100 GROUP BY uid ORDER BY ansnum DESC LIMIT 12;

uid、ansnum均已建索引，主要是GROUP BY uid导致特别慢，如何提速？？？

Answer 1

根据你的查询需求，没有特别好的优化办法。注意group by 和order by用到的字段没办法从索引中受益。除非在where子句中进行条件限制。