mysql 查询 某个字段里内容的总数量和having的用法

1 mysql 查询 某个字段里内容 的总数量

select 字段名, count(*) from 表 group by 字段名

2、having的用法

select ask_id, count(*) from post_answer   group by ask_id having count(*) =1 ORDER  BY ask_id DESC