官网文档：

内链查询

查 site_target_site_group 和 site_target 表中都存在的数据总数

//SELECT count(st.id) from site_target st
//INNER JOIN site_target_site_group tg on tg.site_target_id = st.id
//WHERE tg.site_group_id = 77;

//output  count(st.id) 6

var siteCount int64
e.Orm.Table("site_target as t").
    Select("count(t.id)").
    Joins("inner join site_target_site_group g on g.site_target_id = t.id").
    Where("g.site_group_id = ?", 77).
    Count(&siteCount)

更新文件参考