Oracle 查询根据条件和分组方式连接两个表答案

【问题标题】：Oracle Query to Join Two Tables based on Conditions & Group ByOracle 查询根据条件和分组方式连接两个表
【发布时间】：2021-12-07 11:34:18
【问题描述】：

我有以下格式的表格，

表 1

Bank	Category	Month_Year	Loan_Type	Outstanding
SI	R1	JAN-21	Home	10
SI	R1	JAN-21	Land	50
SI	R2	FEB-21	Home	30
SI	R2	MAR-21	Car	40

表 2

Bank	Loan_Type
SI	Home
SI	Land
SI	Car
SI	Jewel
SI	Education

我想使用连接/查询将表 A 和 B 转换为以下格式。表 2 中的数据（所有行）应根据 Category 和 Month_Year 添加。

BANK	Category	Month_Year	Loan_Type	Outstanding
SI	R1	JAN-21	Home	10
SI	R1	JAN-21	Land	50
SI	R1	JAN-21	Car	0
SI	R1	JAN-21	Jewel	0
SI	R1	JAN-21	Education	0
SI	R2	FEB-21	Home	30
SI	R2	FEB-21	Land	0
SI	R2	FEB-21	Car	0
SI	R2	FEB-21	Jewel	0
SI	R2	FEB-21	Education	0
SI	R2	MAR-21	Home	0
SI	R2	MAR-21	Land	0
SI	R2	MAR-21	Car	40
SI	R2	MAR-21	Jewel	0
SI	R2	MAR-21	Education	0

【问题讨论】：

标签： sql oracle join

【解决方案1】：

创建所需的所有项目的列表并左加入 Table1。例如

select items.Bank, items.Category, items.Month_Year, items.Loan_Type, coalesce(t1.Outstanding, 0) Outstanding
from (
    select t2.Bank, t2.Loan_Type, my.Month_Year,  cat.Category
    from (select distinct Month_Year
          from Table1) my
    cross join (select distinct Category
          from Table1) cat
    cross join Table2 t2
    ) items
left join Table1 t1 on items.Bank = t1.Bank and items.Loan_Type = t1.Loan_Type and items.Month_Year = t1.Month_Year and items.Category = t1.Category;

如果存在表Categories 替换它而不是查询中的派生类别。您可能还希望从参数生成一组 Month_Year 或使用日历表。

【讨论】：

【解决方案2】：

主要是 Category 和 Month_Year 列被明确选择之后的表中需要一个 CROSS JOIN ，并且 Outstanding 列在主查询中添加为零以表示不匹配的值，否则返回它的值作为

SELECT t2.Bank, t2.Category, t2.Month_Year, t2.Loan_Type, 
       NVL(t1.Outstanding,0) AS Outstanding
  FROM (SELECT *
          FROM (SELECT DISTINCT Category, Month_Year FROM table1) 
         CROSS JOIN table2) t2
  LEFT JOIN table1 t1
    ON t2.Category = t1.Category
   AND t2.Month_Year = t1.Month_Year
   AND t2.Loan_Type = t1.Loan_Type
 ORDER BY t2.Category, t2.Month_Year, t1.Outstanding NULLS LAST

Demo

【讨论】：