减少 pl/sql 的过载

Question

我需要对几个属性一一进行匹配。我希望避免使用多个选择语句。下面是例子。

    Table1
    Col1|Price|Brand|size
    -----------------------
    A|10$|BRAND1|SIZE1
    B|10$|BRAND1|SIZE1
    C|30$|BRAND2|SIZE2
    D|40$|BRAND2|SIZE4


    Table2
    Col1|Col2|Col3
    --------------
    B|XYZ|PQR
    C|ZZZ|YYY


    Table3
    Col1|COL2|COL3|LIKECOL1|Price|brand|size
    -----------------------------------------
    B|XYZ|PQR|A|10$|BRAND1|SIZE1
    C|ZZZ|YYY|D|NULL|BRAND2|NULL

在table3中，我需要通过检查以下条件从table2中插入数据。

1. 为表 2 中的记录查找匹配项，如果品牌和尺寸、价格匹配
2. 如果未找到匹配项，则仅尝试品牌、尺寸
3. 仍然找不到匹配项，仅尝试品牌

在上面的示例中，对于 table2 中的第一条记录，发现与所有 3 个属性匹配，因此插入到 table3 和第二条记录中，记录 'D' 匹配但只有 'Brand'。

我能想到的就是将 3 个不同的插入语句（如下所示）写入 oracle pl/sql 块。

 insert into table3 
   select from tab2 
    where all 3 attributes are matching;

 insert into table3 
   select from tab2 
    where brand and price are matching 
      and not exists in table3 (not exists is to avoid 
                                inserting the same record which was already 
                                inserted with all 3 attributes matched);

 insert into table3 
   select from tab2 
    where Brand is matching and not exists in table3;

任何人都可以建议一种更好的方法来以更好的方式实现它，避免多次从 table2 中选择。

Answer 1

这是OUTER APPLY的案例。

OUTER APPLY 是一种横向连接，允许您连接动态视图，这些视图引用出现在 FROM 子句中的表。借助该功能，您可以定义一个动态视图来查找所有匹配项，按您指定的排序顺序对它们进行排序，然后使用FETCH FIRST 1 ROW ONLY 仅将第一个包含在结果中。

使用OUTER APPLY意味着如果没有匹配，你仍然会得到表B记录——只是所有匹配列null。如果不想这样，可以将OUTER APPLY 更改为CROSS APPLY。

这是一个工作示例（一步一步的 cmets），厚颜无耻地从 Michael Piankov 的回答中窃取表创建脚本：

create table Table1 (Col1,Price,Brand,size1)
as select 'A','10','BRAND1','SIZE1' from dual union all
   select 'B','10','BRAND1','SIZE1' from dual union all
   select 'C','30','BRAND2','SIZE2' from dual union all
   select 'D','40','BRAND2','SIZE4'from dual 

create table Table2(Col1,Col2,Col3)
as select 'B','XYZ','PQR' from dual union all 
   select'C','ZZZ','YYY' from dual;

-- INSERT INTO table3
SELECT t2.col1, t2.col2, t2.col3,
t1.col1 likecol1, 
decode(t1.price,t1_template.price,t1_template.price, null) price,
decode(t1.brand,t1_template.brand,t1_template.brand, null) brand,
decode(t1.size1,t1_template.size1,t1_template.size1, null) size1
FROM 
-- Start with table2
table2 t2
-- Get the row from table1 matching on col1... this is our search template
inner join table1 t1_template on
t1_template.col1 = t2.col1
-- Get the best match from table1 for our search 
-- template, excluding the search template itself
outer apply ( 
SELECT * FROM table1 t1 
WHERE 1=1
-- Exclude search template itself
and t1.col1 != t2.col1
-- All matches include BRAND
and t1.brand = t1_template.brand
-- order by match strength based on price and size
order by case when t1.price = t1_template.price and t1.size1 = t1_template.size1 THEN 1
when t1.size1 = t1_template.size1 THEN 2
else 3 END
-- Only get the best match for each row in T2
FETCH FIRST 1 ROW ONLY) t1;

Answer 2

不幸的是，当你说匹配时，你不清楚你的意思是什么。如果有不止一场比赛，你的期望是什么？ 它应该只是第一次匹配还是会生成所有可用的配对？

关于如何避免多次插入的问题不止一种：

1. 您可以使用带有INSERT first 和条件的多表插入。
2. 您可以将 table1 加入 self 并获取所有对并在 where 条件下过滤结果
3. 你可以使用解析函数
4. 我想还有其他方法。但是为什么你想避免 3 个简单的插入。它易于阅读和维护。并且可能是

下面有解析函数的例子：

create table Table1 (Col1,Price,Brand,size1)
as select 'A','10','BRAND1','SIZE1' from dual union all
   select 'B','10','BRAND1','SIZE1' from dual union all
   select 'C','30','BRAND2','SIZE2' from dual union all
   select 'D','40','BRAND2','SIZE4'from dual 

create table Table2(Col1,Col2,Col3)
as select 'B','XYZ','PQR' from dual union all 
   select'C','ZZZ','YYY' from dual

with s as (
select Col1,Price,Brand,size1, 
        count(*) over(partition by Price,Brand,size1 ) as match3, 
        count(*) over(partition by Price,Brand ) as match2,
        count(*) over(partition by Brand ) as match1,
        lead(Col1) over(partition by Price,Brand,size1 order by Col1) as like3, 
        lead(Col1) over(partition by Price,Brand order by Col1) as like2,
        lead(Col1) over(partition by Brand order by Col1) as like1,
        lag(Col1) over(partition by Price,Brand,size1 order by Col1) as like_desc3, 
        lag(Col1) over(partition by Price,Brand order by Col1) as like_desc2,
        lag(Col1) over(partition by Brand order by Col1) as like_desc1
from Table1 t )
select t.Col1,t.Col2,t.Col3, coalesce(s.like3, like_desc3, s.like1, like_desc1, s.like1, like_desc1),
    case when  match3 > 1 then size1 end as size1,
    case when  match1 > 1 then Brand end as Brand,
    case when  match2 > 1 then Price end as Price
        from table2 t
         left join s on s.Col1 = t.Col1 

COL1    COL2    COL3    LIKE_COL    SIZE1   BRAND   PRICE
B   XYZ PQR A   SIZE1   BRAND1  10
C   ZZZ YYY D    -  BRAND2   -