5.筛选
—top n （按个数筛选）
select * from UserInfo
select top 3 * from UserInfo
—top n percent * (按百分比筛选)
select top 20 percent * from UserInfo
—where (行筛选)
select * from UserInfo where UserId=1
—where (列筛选)
select UserName from UserInfo where UserId=1
6.排序
—排序（单重）
select * from UserInfo order by cid desc (—降序-desc，升序-asc)
—排序（多重）
select * from UserInfo order by cid asc,UserPwd desc
–（逗号前为主排序规则，逗号后为子排序规则，即如果前面的相同，则把相同的按照逗号后的规则进行排序）
7.Between … and…语句
—取出编号从2到5的行
select * from UserInfo where UserId between 2 and 5
—取出cid编号为2或5的行
select * from UserInfo where cid in(2,5)