Oracle 视图view

在我看来，oracle的视图就是用于将多个表的关联查询结果映射成【临时表】，视图与系统表中的数据是实时对应的。

我们可以像操作表的查询一样来操作视图查询。

视图写法：

CREATE OR REPLACE FORCE VIEW  V_TEM
(
   ID,
   NAME
)
AS
   SELECT ID,NAME FROM TABLE

项目中的一个案例，将一个自关联的结构表（行转多列）体现组织结构：市-区县-网格-乡镇-渠道

用到的知识点：

1、SYS_CONNECT_BY_PATH(字段,间隔符)    示例：SYS_CONNECT_BY_PATH(ID, '|')

2、SUBSTR()

3、INSTR()

备注：两函数SUBSTR()、INSTR()对待字符串的位置的索引是从1开始的（填写0和1都是代表从第1个位置开始）

 sql代码：

DROP VIEW TLS.V_CHANNEL_PATH;

CREATE OR REPLACE FORCE VIEW TLS.V_CHANNEL_PATH
(
   ID,
   PARENT_ID,
   NAME,
   ID_LEVEL,
   TYPE,
   IN_USE,
   STATUS_TIME,
   LEVEL_ID,
   BANK_NAME,
   ACCOUNT_NAME,
   ACCOUNT_NO,
   GROUP_ID,
   CLASS,
   CHANNEL_TEL,
   QX_CHANNEL_ID,
   PQ_CHANNEL_ID,
   XZ_CHANNEL_ID,
   QX_CHANNEL_NAME,
   PQ_CHANNEL_NAME,
   XZ_CHANNEL_NAME
)
AS
   SELECT ID,
          a.parent_id,
          NAME,
          id_level,
          TYPE,
          in_use,
          status_time,
          level_id,
          bank_name,
          account_name,
          account_no,
          GROUP_ID,
          CLASS,
          channel_tel,
          SUBSTR (a.path_id,
                    INSTR (path_id,
                           '|',
                           1,
                           1)
                  + 1,
                    INSTR (path_id,
                           '|',
                           1,
                           2)
                  - INSTR (path_id,
                           '|',
                           1,
                           1)
                  - 1)
             qx_channel_id,
          SUBSTR (a.path_id,
                    INSTR (path_id,
                           '|',
                           1,
                           2)
                  + 1,
                    INSTR (path_id,
                           '|',
                           1,
                           3)
                  - INSTR (path_id,
                           '|',
                           1,
                           2)
                  - 1)
             pq_channel_id,
          SUBSTR (a.path_id,
                    INSTR (path_id,
                           '|',
                           1,
                           3)
                  + 1,
                    INSTR (path_id,
                           '|',
                           1,
                           4)
                  - INSTR (path_id,
                           '|',
                           1,
                           3)
                  - 1)
             xz_channel_id,
          SUBSTR (a.path_name,
                    INSTR (path_name,
                           '|',
                           1,
                           1)
                  + 1,
                    INSTR (path_name,
                           '|',
                           1,
                           2)
                  - INSTR (path_name,
                           '|',
                           1,
                           1)
                  - 1)
             qx_channel_name,
          SUBSTR (a.path_name,
                    INSTR (path_name,
                           '|',
                           1,
                           2)
                  + 1,
                    INSTR (path_name,
                           '|',
                           1,
                           3)
                  - INSTR (path_name,
                           '|',
                           1,
                           2)
                  - 1)
             pq_channel_name,
          SUBSTR (a.path_name,
                    INSTR (path_name,
                           '|',
                           1,
                           3)
                  + 1,
                    INSTR (path_name,
                           '|',
                           1,
                           4)
                  - INSTR (path_name,
                           '|',
                           1,
                           3)
                  - 1)
             xz_channel_name
     FROM (    SELECT a.*,
                      SUBSTR (SYS_CONNECT_BY_PATH (ID, '|'), 2) || '|' path_id,
                      SUBSTR (SYS_CONNECT_BY_PATH (NAME, '|'), 2) || '|'
                         path_name
                 FROM tl_channel a
           START WITH ID = 1
           CONNECT BY PRIOR ID = parent_id) a;