SQL语句：用count求group by分组的个数

1、创建测试表，create table test_group(pid number, sid varchar2(20));

2、插入测试数据，

insert into test_group values(1,'001');

insert into test_group values(2,'001');

insert into test_group values(2,'002');

insert into test_group values(2,'002');

insert into test_group values(2,'002');

insert into test_group values(3,'003');

insert into test_group values(3,'003');

insert into test_group values(null,'004');

3、查询表中记录，select t.*, rowid from test_group t;

4、编写sql，将记录分组后，记录组数，结果为4组，

select count(*) from (select count(*) num,sid from test_group group by sid)

select count(*) num,sid into #a from person group by sid
select count(*) from #a

或者
select count(*) from (select count(*) num,sid from person group by sid )

from括号后面要带重命名
select count(*) from (select count(*) num,sid from person group by sid ) rename

select count(*) from (select sid from person group by sid) s;