SQL知识整理

一：Select语句：
       select 字段名 from 表名 where 条件 order by 排序
see:select distinct 从多个相同字段中抓唯一值    
see:查找ld_det_andy表中有数据但ld_det_temp表中没数据的数据
        select * from ld_det_andy a where
       (not exists (select * from ld_det_temp where ld_loc = a.ld_loc and ld_part = a.ld_part))
see:选出累计访问量最大的10个ip地址，并按访问量降序排列。
        select top 10 ip, countip from
       (select ip,count(*) as countip from records group by ip) a
       order by countip desc
see:表student(id,name,score)根据分数列（score）每10分为一段，查询每段分数的人数
        select ScoreRank,count(*) from
       (select ScoreRank = case
         when score >= 0   and score < 10   then '0-9'
         when score >= 10 and score < 20   then '10-19'
         when score >= 20 and score < 30   then '20-29'
         when score >= 30 and score < 40   then '30-39'
         when score >= 40 and score < 50   then '40-49'
         when score >= 50 and score < 60   then '50-59'
          when score >= 60 and score < 70   then '60-69'
         when score >= 70 and score < 80   then '70-79'
         when score >= 80 and score < 90   then '80-89'
  &nb