進展してないのでしょうか?ある程度ご自身の中の回答もまとまったでしょうから参考までに
テーブル作成
SQL
1create table states(
2sid int primary key,
3sname varchar(20),
4area int);
5insert into states values
6(2,'AOMORI',30),
7(40,'FUKUOKA',5),
8(34,'HIROSHIMA',8),
9(15,'NIGATA',13);
10
11create table clients(
12cid varchar(20) primary key,
13cname varchar(20),
14capital int,
15sid int,
16foreign key (sid)
17references states(sid));
18insert into clients values
19('A01','NAOMI',45,2),
20('A02','TAEKO',30,2),
21('B04','AKIRA',50,15),
22('B03','KEIKO',40,40),
23('B01','SATORU',25,15);
設問
SQL
1/* (a) */
2select cid,cname,capital
3from clients
4where sid<>15
5order by capital asc;
6
7/* (b) */
8select sid,avg(capital)
9from clients
10group by sid
11order by sid asc;
12
13/* (c) */
14select
15t1.cid,t1.cname,t2.sname
16from clients as t1
17inner join states as t2
18on t1.sid=t2.sid
19where t1.capital>=40
20order by cid asc;