Question

我想得到孩子的数量。我尝试这个查询，但没有工作 table colums

ID， father_id，名字

select id As parent_id , father_id ,name, count(select * from users WHERE father_id = parent_id) As child
        from users

Answer 1

使用相关的子查询来计算：

select id As parent_id , father_id ,name, (select count(*) from users u2
                                           WHERE u2.father_id = u1.id) As child
from users u1

Answer 2

您正在使用表格users两次。使用表别名来显示您正在谈论的两个记录：

select 
  id as parent_id, 
  father_id,
  name, 
  (select count(*) from users c where c.father_id = p.id) as children
from users p;

Answer 3

尝试使用group_by子句。

select id as parent_id，father_id，name，count（select * from users WHERE father_id = parent_id）as child 来自parent_id的用户组

Answer 4

您是否尝试过此操作，而不是使用*，获取您想要计算的特定字段：

    select id As parent_id , father_id ,name, count(select name from users WHERE father_id = parent_id) As child
    from users

如何计算用户的子女数量

4 个答案: