複数の特定の列データの選択

Question

複数回繰り返されるgno内のすべての項目を選択する必要があります。つまり、この場合1001を選択できる必要があります。

create table project99 
(
pno int primary key, 
projtitle varchar2(30), 
projarea varchar2(30), 
startd date, 
gno int references guide99(gno) 
); 

insert into project99 values(1,'E Commerce website','php','03-jan-2016',1001); 
insert into project99 values(2,'Web forums','php','05-jan-2016',1001); 
insert into project99 values(3,'Sudoku','C','06-jan-2016',1002); 
insert into project99 values(4,'Student management System','php','04-jan-2016',1003); 
insert into project99 values(5,'Antivirus','System','04-jan-2016',1004); 
insert into project99 values(6,'Snake','C++','03-jan-2016',1004); 
insert into project99 values(7,'Library management','php','03-jan-2016',1006); 
insert into project99 values(8,'Video Sharing website','C#','03-jan-2016',1005); 
insert into project99 values(9,'Search Algorithm','maths','03-may-2016',1010); 
insert into project99 values(10,'Email','php','03-jan-2016',1007); 

Answer 1

SELECT gno 
    FROM project99 
GROUP BY gno 
HAVING COUNT(1) > 1;