Oracle面试题1

题目：有一张老师表T，字段是T_ID，T_NAME；有一张学生表S，字段是S_ID，S_NAME；还有一张班级表C，字段是T_ID，S_ID，C_NAME，其中C_NAME的取值只有‘大班’和‘小班’，请查询出符合条件的老师的名字，条件是老师在大班中带的学生数大于老师在小班中带的学生数

--建立T表

create table T(
t_id number(4) primary key,
t_name varchar2(20)); 

--建立S表

create table S(
s_id number(4) primary key,
s_name varchar2(20));

--建立C表

 create table C(
 t_id number(4) references T(t_id),
 s_id number(4) references S(s_id),
 c_name char(6) check(c_name in ('大班','小班')));

--插入数据

--T表
 insert into T values(1,'A');
 insert into T values(2,'B');
--S表
 insert into S values(11,'1A');
 insert into S values(12,'1B');
 insert into S values(13,'1C');
 insert into S values(14,'1D');
 insert into S values(15,'1E');
 insert into S values(16,'1F');
 insert into S values(17,'1G');
 insert into S values(18,'1H');
--C表
 insert into C values(1,11,'大班');
 insert into C values(1,12,'大班');
 insert into C values(1,17,'大班');
 insert into C values(1,16,'大班');
 insert into C values(1,13,'小班');
 insert into C values(1,14,'小班');
 insert into C values(1,15,'小班');
 insert into C values(2,18,'小班');

--SQL语句

select 
  t_name 
from t 
where t_id in (
      select distinct c1.t_id from c c1
      where 
       (select count(*) from c c2 
               where c2.t_id = c1.t_id and c2.c_name='大班')
       >(select count(*) from c c3 
               where c3.t_id = c1.t_id and c3.c_name='小班'))

--查询结果

T_NAME
--------------------
A