SQL学习备忘

1.按照拼音首字母的正序或倒序排序

SELECT
    CREATOR_REALNAME
FROM
    tableName
ORDER BY NLSSORT(CREATOR_REALNAME, 'NLS_SORT = SCHINESE_PINYIN_M') desc

参考：nls_sort和nlssort 排序功能介绍

2.按照创建时间降序排序：即按照创建时间从大道小排序，（时间从数轴上看，最新时间在右，就越大，老时间在左，就越小）；所以按照创建时间降序排序的结果就是最新的数据在前，老数据在后；

ORDER BY CREATE_TIME DESC,MODEL_NAME ASC

3.CASE 语句的使用：

select p.wb_id as 工作包ID, p.wb_name as 工作包名称,m.model_id as 项目ID, m.model_name as 项目名称,
       case m.model_flag when '0' then '基础WBS' when '1' then '项目WBS' end as 所属WBS
  from km_process p, km_model_info m
 where p.model_id=m.model_id
   and p.wb_id='20130911000348'

4.三层结构+查询的条数，分装的Oracle的分页查询

SELECT *
  FROM (SELECT COUNT(1) CNT
          FROM (SELECT case r.rela_table_tag
                         when 'process_piture' then
                          '图片文件'
                         when 'process_visio' then
                          'Visio文件'
                       end as rela_table_tag,
                       r.rela_table_code rela_table_code,
                       f.file_id file_id,
                       f.file_path file_path,
                       f.original_file_name original_file_name,
                       f.ext_name ext_name,
                       f.model_id modelId,
                       f.phase_name phase_name
                  FROM KM_PROCESS_PICTURE_RELA r, KM_FILE_INFO f
                 WHERE r.file_id = f.file_id
                   AND r.rela_table_code = '20141014944972'
                 ORDER BY f.create_time desc)),
       (SELECT rela_table_tag,
               rela_table_code,
               file_id,
               file_path,
               original_file_name,
               ext_name,
               modelId,
               phase_name
          FROM (SELECT rela_table_tag,
                       rela_table_code,
                       file_id,
                       file_path,
                       original_file_name,
                       ext_name,
                       modelId,
                       phase_name,
                       ROWNUM AS MY_ROWNUM
                  FROM (SELECT case r.rela_table_tag
                                 when 'process_piture' then
                                  '图片文件'
                                 when 'process_visio' then
                                  'Visio文件'
                               end as rela_table_tag,
                               r.rela_table_code rela_table_code,
                               f.file_id file_id,
                               f.file_path file_path,
                               f.original_file_name original_file_name,
                               f.ext_name ext_name,
                               f.model_id modelId,
                               f.phase_name phase_name
                          FROM KM_PROCESS_PICTURE_RELA r, KM_FILE_INFO f
                         WHERE r.file_id = f.file_id
                           AND r.rela_table_code = '20141014944972'
                         ORDER BY f.create_time desc))
         WHERE MY_ROWNUM <= 10
           AND MY_ROWNUM > 0)

5.decode函数的使用

   SELECT  p.PHASE_ID,
            p.PHASE_NAME, 
            p.PHASE_CODE, 
                p.MODEL_ID,
                p.SOURCE_DATA_ID, 
                decode(h.parent_id,null ,'-1', h.parent_id) PARENT_ID
            FROM  RDM_MODEL_PHASE p, erm_basic_dataitem_view h
         WHERE  p.DELETE_FLAG = '0'
           AND  p.SOURCE_DATA_ID = h.PHASE_ID
           AND  p.MODEL_ID = ?

6.Right,Left

-- 39   
select i.phase_id,
       decode(j.source_data_id,null,'-1',j.source_data_id) parent_id,
       i.phase_name,
       i.source_data_id
  from RDM_MODEL_PHASE i left join RDM_MODEL_PHASE j on i.parent_id=j.phase_id
 where i.delete_flag = '0'
   and i.model_id = '141352764572700067'
   
-- 11   
select i.phase_id,
       decode(j.source_data_id,null,'-1',j.source_data_id) parent_id,
       i.phase_name,
       i.source_data_id
  from RDM_MODEL_PHASE i right join RDM_MODEL_PHASE j on i.parent_id=j.phase_id
 where i.delete_flag = '0'
   and i.model_id = '141352764572700067' 
   
     --  39  11  28  
--原始 39           
select i.phase_id,i.parent_id, i.phase_name,i.source_data_id
  from RDM_MODEL_PHASE i 
 where i.delete_flag = '0'
   and i.model_id = '141352764572700067' 

7.sql查找最小缺失值与重用被删除的键

8.Coalesce函数

9.oracle中的exists 和not exists 用法