a)
SELECT *
FROM video
WHERE vid=35
结果：
b)
SELECT user.*
FROM user JOIN post ON user.uid = post.uid
WHERE post.vid = 35
结果：
c)
SELECT count(*)
FROM watch
WHERE vid=35
结果：
d)
SELECT count(*)
FROM like
WHERE vid=35
结果：
e)
SELECT count(*)
FROM collect
WHERE vid=35
结果：
f)
SELECT sum(coin.amount)
FROM coin
WHERE vid=35
结果：
g)
SELECT *
FROM comment
WHERE vid=35
ORDER BY video_time ASC
结果：
SELECT user.nickname,count(post.vid)
FROM user JOIN post ON user.uid = post.uid
GROUP BY user.uid, user.nickname
ORDER BY count(post.vid) DESC
LIMIT 5
结果：
SELECT user.nickname,user.profile,user.userlevel, count(follow.uid_followed)
FROM user JOIN follow ON user.uid = follow.uid_followed
GROUP BY user.nickname,user.profile,user.userlevel
ORDER BY count(follow.uid_followed) DESC
LIMIT 10
结果：
SELECT video.name,video.description,count(watch.vid)
FROM video JOIN watch ON video.vid = watch.vid
GROUP BY video.name,video.description,video.vid
ORDER BY count(watch.vid) DESC
LIMIT 10
结果：
SELECT video.chanel,count(watch.vid)
FROM video JOIN watch ON video.vid = watch.vid
GROUP BY video.chanel
结果：
SELECT video.name,count(watch.uid)
FROM watch JOIN video ON watch.vid = video.vid
WHERE video.chanel = '美食'
GROUP BY video.vid
ORDER BY count(watch.uid) DESC
LIMIT 5
结果：
SELECT video.chanel,count(watch.vid)
FROM watch JOIN video ON watch.vid = video.vid
WHERE watch.uid = 15
GROUP BY video.chanel
ORDER BY count(watch.vid) DESC
LIMIT 5
结果：
SELECT video.name,video.description
FROM user JOIN watch ON watch.uid = user.uid
JOIN video ON watch.vid = video.vid
WHERE user.uid = 15 AND watch.time > 900
结果：
SELECT user.nickname,user.profile,user.userlevel
FROM user JOIN follow ON user.uid = follow.uid_follower
WHERE follow.uid_followed = 15
结果：
SELECT video.name,video.description,post.post_time
FROM video JOIN post ON video.vid = post.vid
JOIN follow ON post.uid=follow.uid_followed
WHERE follow.uid_follower = 15
ORDER BY post.post_time DESC
结果：
SELECT user.nickname,user.profile,user.userlevel
FROM user JOIN follow f1 ON user.uid = f1.uid_followed
JOIN follow f2 ON user.uid = f2.uid_follower
WHERE f1.uid_follower = 15 AND f2.uid_followed = 15
结果：
