Oracle sql语法错误，

sql 如下：
select count(x.*) from sck_kz x,(select user_id from sck_kz group by user_id having count(distinct mobile)=1) y where x.user_id=y.user_id;
求解
错误提示：ORA-01747: invalid user.table.column, table.column, or column specification

答案：select a.* from (select user_id,count(x.*) from sck_kz x group by user_id) a inner join 
(select user_id from sck_kz group by user_id having count(distinct mobile)=1) y on a.user_id=y.user_id;

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