optimize.md

MySQL Optimize

• count 和 group by优化

    SELECT
    	count(*) AS num,
    	create_type AS type
    FROM
    	table_name
    WHERE
    	create_at > '2017-06-05'
    AND create_at < '2017-07-05'
    GROUP BY
    	create_type;
  

  建立索引：

    CREATE INDEX create_at_type ON table_name (create_type, create_at);
  

  PS:尽量使varchar字段更小。