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mysql count group by统计条数方法

mysql 分组之后如何统计记录条数? gourp by 之后的 count，把group by查询结果当成一个表再count一次
select count(*) as count from
(SELECT count(*) FROM 表名 WHERE 条件 GROUP BY id ) a;

实战例子：
select 
count(*) as total 
from (select count(*) from users group by user_id) u

SELECT count(*) from (SELECT post_ask.ask_id,post_ask.ask_body,post_ask.ask_user,post_answer.answer_body,post_answer.answer_user  from post_ask right JOIN post_answer on post_ask.ask_id = post_answer.ask_id and post_answer.answer_body is not null where post_ask.ask_id is not null and post_ask.ask_body <>''  GROUP BY post_ask.ask_id ) as u