Oracle 连接视图以获得最佳匹配

Question

我想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

所以在这些示例中，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)

我遇到的困难是在它符合多个规则的情况下（例如第 1 行和第 3 行符合规则 1 和 2，或者第 4 行和第 6 行分别符合规则 2 和 3）。

我在这个例子中意识到规则 3 被多次命中 - 这很好，因为它只会在其他规则不正确时才命中规则 3，应该只产生 1 个结果（如示例 3）。

有没有办法做一个类似的联合来满足这些级联规则，或者是否需要通过预过滤（例如计数 < 2）来创建额外的视图？

excel 中的公式为： =IF(AND(A3=$F$2,B3=$G$2),"Rule1",IF((B3=$G$2),"Rule 2",IF((A3=$F$2), "Rule 3","NULL")))

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

Answer 1

也许是这个方法，它将三个常见 table 表达式的结果集链接在一起，每个表达式都实现了不同的连接，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

Answer 2

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（在本例中，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替代方案，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

N.B。如果碰巧有不止一行满足最高优先级的可用连接条件，这些结果可能 return 不同。第一个查询将 return 每行具有（可能）不同的 col3，而第二个查询将 return 只有一行，具有最低的可用 col3 值。

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

Oracle 连接视图以获得最佳匹配

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