Oracle 加入视图以获得最佳匹配

Question

我希望创建一个将两个表连接在一起的视图。

T1 =

Col1 Col2
AA   BB
EE   FF
YY   ZZ
11   00

T2 =

Col1 Col2 Col3
AA   BB   1
AA   CC   2
CC   BB   3
GG   FF   4
GG   HH   5
EE   HH   6
XX   YY   7
XX   WW   8
YY   RR   9

此视图的规则是基于以下规则的最佳匹配方案：

1. Return Col3 from T2 if T1.Col1 & T1.Col2 = T2.Col1 & T2.Col2
ELSE
2. Return Col3 if T1.Col2 = T2.Col2
ELSE
3. Return Col3 if T1.Col = T2.Col1
ELSE
4. Return NULL

因此，在这些示例中，我希望最终视图包含：

AA BB 1   (Rule 1 match)
EE FF 4   (Rule 2 match)
YY ZZ 9   (Rule 3 match)
11 00 NULL (Rule 4 match)

我遇到的困难在于它满足多个规则的情况（例如，第 1 行和第 3 行，其中规则 1 和 2 被击中，或者第 4 和 6 行，其中规则 2 和 3 分别被击中）。

我意识到在这个例子中规则 3 被多次命中 - 这很好，因为它只会在其他规则不正确时才会命中规则 3，而 应该 只产生 1结果（如示例 3 所示）。

有没有办法进行类似的联合来满足这些级联规则，或者是否需要使用预过滤创建额外的视图（例如计数

excel 中的一个公式是： =IF(AND(A3=$F$2,B3=$G$2),"规则 1",IF((B3=$G$2),"规则 2",IF((A3=$F$2),"规则 3 ","NULL")))

其中 A3 = T2.Col1，B3 = T2.Col2 G2 = T1.Col2 和 F2 = T1.Col1。

Answer 1

我会这样做：

with t1 as (select 'AA' col1, 'BB' col2 from dual union all
            select 'EE' col1, 'FF' col2 from dual union all
            select 'YY' col1, 'ZZ' col2 from dual union all
            select '11' col1, '00' col2 from dual),
     t2 as (select 'AA' col1, 'BB' col2, 1 col3 from dual union all
            select 'AA' col1, 'CC' col2, 2 col3 from dual union all
            select 'CC' col1, 'BB' col2, 3 col3 from dual union all
            select 'GG' col1, 'FF' col2, 4 col3 from dual union all
            select 'GG' col1, 'HH' col2, 5 col3 from dual union all
            select 'EE' col1, 'HH' col2, 6 col3 from dual union all
            select 'XX' col1, 'YY' col2, 7 col3 from dual union all
            select 'XX' col1, 'WW' col2, 8 col3 from dual union all
            select 'YY' col1, 'RR' col2, 9 col3 from dual),
    res as (select t1.col1,
                   t1.col2,
                   t2.col3,
                   case when t1.col1 = t2.col1 and t1.col2 = t2.col2 then 1
                        when t1.col2 = t2.col2 then 2
                        when t1.col1 = t2.col1 then 3
                   end join_level,
                   min (case when t1.col1 = t2.col1 and t1.col2 = t2.col2 then 1
                             when t1.col2 = t2.col2 then 2
                             when t1.col1 = t2.col1 then 3
                        end) over (partition by t1.col1, t1.col2) min_join_level
            from   t1
                   left outer join t2 on (t1.col1 = t2.col1 or t1.col2 = t2.col2))
select col1,
       col2,
       col3
from   res
where  join_level = min_join_level
or     join_level is null;


COL1 COL2       COL3
---- ---- ----------
11   00                                       
AA   BB            1
EE   FF            4
YY   ZZ            9

即。首先进行连接（在这种情况下，t1 left outer join t2 on (t2.col1 = t1.col1 or t2.col2 = t1.col2) 包括 t1.col1 = t2.col1 and t1.col2 = t2.col2 所在的行），然后根据哪个连接条件优先过滤结果。

---

这里有一个稍微不同的选择，使用聚合而不是像上面的答案那样的分析函数：

with t1 as (select 'AA' col1, 'BB' col2 from dual union all
            select 'EE' col1, 'FF' col2 from dual union all
            select 'YY' col1, 'ZZ' col2 from dual union all
            select '11' col1, '00' col2 from dual),
     t2 as (select 'AA' col1, 'BB' col2, 1 col3 from dual union all
            select 'AA' col1, 'CC' col2, 2 col3 from dual union all
            select 'CC' col1, 'BB' col2, 3 col3 from dual union all
            select 'GG' col1, 'FF' col2, 4 col3 from dual union all
            select 'GG' col1, 'HH' col2, 5 col3 from dual union all
            select 'EE' col1, 'HH' col2, 6 col3 from dual union all
            select 'XX' col1, 'YY' col2, 7 col3 from dual union all
            select 'XX' col1, 'WW' col2, 8 col3 from dual union all
            select 'YY' col1, 'RR' col2, 9 col3 from dual)
select t1.col1,
       t1.col2,
       min(t2.col3) keep (dense_rank first order by case when t1.col1 = t2.col1 and t1.col2 = t2.col2 then 1
                                                         when t1.col2 = t2.col2 then 2
                                                         when t1.col1 = t2.col1 then 3
                                                    end) col3
from   t1
       left outer join t2 on (t1.col1 = t2.col1 or t1.col2 = t2.col2)
group by t1.col1,
         t1.col2;

COL1 COL2       COL3
---- ---- ----------
11   00             
AA   BB            1
EE   FF            4
YY   ZZ            9

注意如果碰巧有不止一行满足最高优先级的可用连接条件，这些可能会返回不同的结果。第一个查询将返回具有（可能）不同的 col3 的每一行，而第二个查询将只返回一个具有最低可用 col3 值的行。

---

如果 T2 包含，您希望看到什么：

COL1 COL2       COL3
---- ---- ----------
AA   BB            1
AA   CC            2
CC   BB            3
GG   FF            4
GG   HH            5
EE   HH            6
XX   YY            7
XX   WW            8
YY   RR            9
YY   SS           10

第一个查询会给你：

COL1 COL2       COL3
---- ---- ----------
11   00             
AA   BB            1
EE   FF            4
YY   ZZ           10
YY   ZZ            9

第二个查询会给你：

COL1 COL2       COL3
---- ---- ----------
11   00             
AA   BB            1
EE   FF            4
YY   ZZ            9

Answer 2

也许是这个方法，它将三个公共表表达式的结果集链接在一起，每个表达式实现不同的连接并检查 T1 中行的 rowid 是否已经从成功的连接中投影出来：

with
  first_join as (
    select t1.col1,
           t1.col2,
           t2.col3,
           t1.rowid
    from   t1 join t2 on t1.col1 = t2.col1 and t1.col2 = t2.col2),
  second_join as (
    select t1.col1,
           t1.col2,
           t2.col3,
           t1.rowid
    from   t1 join t2 on  t1.col2 = t2.col2
    where  t1.rowid not in (select rowid from first_join)),
  third_join as (
      select t1.col1,
             t1.col2,
             t2.col3,
      from   t1 join t2 on  t1.col1 = t2.col1
      where  t1.rowid not in (select rowid from first_join union all
                              select rowid from second_join))
select col1, col2, col3 from first_join  union all
select col1, col2, col3 from second_join union all
select col1, col2, col3 from third_join