谁帮我做下下面三道题 做不出来啊

[pps230]

Sailors(sid:integer, sname:string, rating:integer, age:real)
Boats(bid:integer, bname:string, color:string)
Reserves(sid:integer, bid:integer, day:date)
Sailors（水手表）
sid编号 same名字 rating等级 age年龄
22 Dustin 7 45.0
29 Brutus 1 33.0
31 Lubber 8 55.5
32 Andy 8 25.5
58 Rusty 10 35.0
64 Horatio 7 35.0
71 Zorba 10 16.0
74 Horatio 9 35.0
85 Art 3 25.5
95 Bob 3 63.5
Reserves（预订情况表）
sid水手编号bid船只编号day日期
22 101 10/10/98
22 102 10/10/98
22 103 10/8/98
22 104 10/7/98
31 102 11/10/98
31 103 11/6/98
31 104 11/12/98
64 101 9/5/98
64 102 9/8/98
74 103 9/8/98
Boats（船只表）
bid编号 bname名字 color颜色
101 Interlake blue
102 Interlake red
103 Clipper green
104 Marine red




1.对于至少有两个水手的等级级别，求出水手们的平均年龄
2.对于至少有两个水手的等级，找出到了投票年龄（至少有18岁）的所有水手的平均年龄
3.找出在所有的等级中水手的平均年龄是最低的那些等级

[DBA_磊仔]

--构建示例数据 drop table Sailors
Create TABLE Sailors (sid int,same varchar(50),rating int,age numeric(32,2))
INSERT INTO Sailors select '22', 'Dustin', '7', '45.0'
      union all select '29', 'Brutus', '1', '33.0'
      union all select '31', 'Lubber', '8', '55.5'
      union all select '32', 'Andy', '8', '25.5'
      union all select '58', 'Rusty', '10', '35.0'
      union all select '64', 'Horatio', '7', '35.0'
      union all select '71', 'Zorba', '10', '16.0'
      union all select '74', 'Horatio', '9', '35.0'
      union all select '85', 'Art', '3', '25.5'
      union all select '95', 'Bob', '3', '63.5'     

--方案
--1.对于至少有两个水手的等级级别，求出水手们的平均年龄
select rating,AVG(age) avgage from Sailors group by rating having COUNT(same) >= 2
/*rating      avgage
----------- ---------------------------------------
3           44.500000
7           40.000000
8           40.500000
10          25.500000

(4 行受影响)

*/
--2.对于至少有两个水手的等级，找出到了投票年龄（至少有18岁）的所有水手的平均年龄
select rating,AVG(age) avgage from Sailors 
where rating in(select rating from Sailors group by rating having COUNT(same) >= 2)
and age >= 18 group by rating
/*
rating      avgage
----------- ---------------------------------------
3           44.500000
7           40.000000
8           40.500000
10          35.000000

(4 行受影响)


*/
--3.找出在所有的等级中水手的平均年龄是最低的那些等级
select TOP(1) rating,AVG(age) avgage from Sailors group by rating ORDER BY AVG(age)
/*rating      avgage
----------- ---------------------------------------
10          25.500000

(1 行受影响)

*/