如何在两个表之间的组中实现这种递归连接？

Question

我在一个名为的表中有一些混乱的数据AVAILABLE_TEMPLATES.这是一个简单的例子:

TEMPLATE_GROUP TEMPLATE_NAME LOCALE
-------------- ------------- ------
RO              LTRU          fi_FI  
RO              LTRU          se_SE  
RO              LTRU          en_US  
BL              V1PRO         se_SE  
BL              V1PRO         en_US  

我有另一个包含语言环境的表SYSTEM_LOCALES.

SYS_LOCALE
------
lv_LV  
fi_FI  
sv_SE  
en_US

我希望看到通过连接这两个表应该在该行的笛卡尔积得到的数据SYS_LOCALE表和不同TEMPLATE_GROUP/ TEMPLATE_NAME从AVAILABLE_TEMPLATES表.

我们的默认语言环境是fi_FI.对于每TEMPLATE_NAME一个TEMPLATE_GROUP,我想检查是否匹配的语言环境是可用的,如果是,就应该退还USE_LOCALE.如果找不到匹配的语言环境,我想返回系统的默认语言环境,即fi_FI它是否存在于TEMPLATE_NAME和TEMPLATE_GROUPas USE_LOCALE.

这是加入两个表应该返回的内容:

TEMPLATE_GROUP TEMPLATE_NAME SYS_LOCALE  USE_LOCALE
-----------    ------------- ------      ----------
RO             LTRU          lv_LV       fi_FI      --There's a fi_FI locale but no lv_LV 
RO             LTRU          fi_FI       fi_FI    
RO             LTRU          se_SE       se_SE    
RO             LTRU          en_US       en_US    
BL             V1PRO         lv_LV       NULL       --There's no lv_LV or a fi_FI locale 
BL             V1PRO         fi_FI       NULL       --There's no fi_FI locale
BL             V1PRO         se_SE       se_SE    
BL             V1PRO         en_US       en_US    

我无法想象这一个,并且已经完全失去了机智.它是否必须通过递归完成？谢谢

Answer 1

允许您在不多次读取表的情况下执行此操作的唯一构造是分区外连接.

以下是您的数据集的示例:

SQL> create table available_templates (template_group,template_name,locale)
  2  as
  3  select 'RO', 'LTRU', 'fi_FI' from dual union all
  4  select 'RO', 'LTRU', 'se_SE' from dual union all
  5  select 'RO', 'LTRU', 'en_US' from dual union all
  6  select 'BL', 'V1PRO', 'se_SE' from dual union all
  7  select 'BL', 'V1PRO', 'en_US' from dual
  8  /

Table created.

SQL> create table system_locales (sys_locale)
  2  as
  3  select 'lv_LV' from dual union all
  4  select 'fi_FI' from dual union all
  5  select 'se_SE' from dual union all
  6  select 'en_US' from dual
  7  /

Table created.

和分区外连接:

SQL> select at.template_group
  2       , at.template_name
  3       , sl.sys_locale
  4       , nvl
  5         ( at.locale
  6         , max(decode(at.locale,'fi_FI',at.locale)) over (partition by at.template_group, at.template_name)
  7         ) use_locale
  8    from system_locales sl
  9         left outer join available_templates at
 10           partition by (at.template_group,at.template_name)
 11           on (at.locale = sl.sys_locale)
 12  /

TEMPLATE_GROUP TEMPLATE_NAME SYS_LOCALE USE_LOCALE
-------------- ------------- ---------- ----------
BL             V1PRO         en_US      en_US
BL             V1PRO         fi_FI
BL             V1PRO         lv_LV
BL             V1PRO         se_SE      se_SE
RO             LTRU          en_US      en_US
RO             LTRU          fi_FI      fi_FI
RO             LTRU          lv_LV      fi_FI
RO             LTRU          se_SE      se_SE

8 rows selected.

以下是表格仅扫描一次的证据:

    SQL> select * from table(dbms_xplan.display_cursor(null,null,'allstats last'))
      2  /

    PLAN_TABLE_OUTPUT
    ---------------------------------------------------------------------------------------------------------------------------------------
    SQL_ID  57br33gc6n1sc, child number 0
    -------------------------------------
    select at.template_group      , at.template_name      , sl.sys_locale
       , nvl        ( at.locale        ,
    max(decode(at.locale,'fi_FI',at.locale)) over (partition by
    at.template_group, at.template_name)        ) use_locale   from
    system_locales sl        left outer join available_templates at
     partition by (at.template_group,at.template_name)          on
    (at.locale = sl.sys_locale)

    Plan hash value: 921719364

-----------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                    | Name                | Starts | E-Rows | A-Rows |   A-Time   | Buffers |  OMem |  1Mem | Used-Mem |
-----------------------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |                     |      1 |        |      8 |00:00:00.01 |       6 |       |       |          |
|   1 |  WINDOW BUFFER               |                     |      1 |      1 |      8 |00:00:00.01 |       6 |  2048 |  2048 | 2048  (0)|
|   2 |   VIEW                       |                     |      1 |      1 |      8 |00:00:00.01 |       6 |       |       |          |
|   3 |    MERGE JOIN PARTITION OUTER|                     |      1 |      1 |      8 |00:00:00.01 |       6 |       |       |          |
|   4 |     SORT JOIN                |                     |      3 |      4 |      9 |00:00:00.01 |       3 |  2048 |  2048 | 2048  (0)|
|   5 |      TABLE ACCESS FULL       | SYSTEM_LOCALES      |      1 |      4 |      4 |00:00:00.01 |       3 |       |       |          |
|*  6 |     SORT PARTITION JOIN      |                     |      9 |      5 |      5 |00:00:00.01 |       3 |  2048 |  2048 | 2048  (0)|
|   7 |      TABLE ACCESS FULL       | AVAILABLE_TEMPLATES |      1 |      5 |      5 |00:00:00.01 |       3 |       |       |          |
-----------------------------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   6 - access("AT"."LOCALE"="SL"."SYS_LOCALE")
       filter("AT"."LOCALE"="SL"."SYS_LOCALE")

Note
-----
   - dynamic sampling used for this statement (level=2)


35 rows selected.

问候,
Rob.