Mysql count(1) group_concat 高级用法(count 过滤条件，group_concat过滤条件)

1、官方文档：

count：COUNT(expr) [over_clause]

https://dev.mysql.com/doc/refman/8.0/en/group-by-functions.html#function_count

1.1 实例：

select update_time,sid,group_concat(if(age > '1', tid, NULL)),count(DISTINCT if(age =1,tid,null)) as current_t

from tb_s_members group by update_time,sid order by update_time desc

 select a.gid,a.t_m,ifnull(b.h_c,0) as hc,(a.t_m-ifnull(b.h_c,0)) as l_c from 
(select mem.gid as gid,count(distinct mid) as t_m from members mem group by gid) as a left join 
(select gid,count(distinct mid) as h_c from members_history group by gid) as b on a.gid = b.gid;

2、group_concat 官方文档：

GROUP_CONCAT([DISTINCT] expr [,expr ...]
             [ORDER BY {unsigned_integer | col_name | expr}
                 [ASC | DESC] [,col_name ...]]
             [SEPARATOR str_val])

https://dev.mysql.com/doc/refman/8.0/en/group-by-functions.html#function_group-concat