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

拼音排序

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 '' then '基础WBS' when '' 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=''

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 = ''
                  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 = ''
                          ORDER BY f.create_time desc))
          WHERE MY_ROWNUM <= 10
            AND MY_ROWNUM > 0)

Oracle分页查询

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 = ''
            AND  p.SOURCE_DATA_ID = h.PHASE_ID
            AND  p.MODEL_ID = ?

decode

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 = ''
    and i.model_id = ''

 -- 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 = ''
    and i.model_id = '' 

      --  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 = ''
    and i.model_id = '' 

Right,Left左右关联查询

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