Question

我需要在Linq-to-sql中实现

SELECT DISTINCT c.*
FROM dbo.Collector_Capital_Equipment c
LEFT OUTER JOIN dbo.Lab_Space s ON c.Room = s.Entry_Bar_Code 
                                OR c.HomeRoom = s.Entry_Bar_Code
WHERE s.id = 1021645

我对此所做的所有研究都表明linq-to-sql无法支持“或”多重联接，建议采取这样的两种联接：

SELECT DISTINCT c.*
FROM dbo.Collector_Capital_Equipment c
LEFT OUTER JOIN dbo.Lab_Space s ON c.Room = s.Entry_Bar_Code 
LEFT OUTER JOIN dbo.Lab_Space s2 ON c.HomeRoom = s2.Entry_Bar_Code
WHERE s.id = 1021645

尽管这些查询将返回不同的结果，但它们实际上不是相同的查询。到目前为止，除了将原始SQL放入我的C＃程序之外，还有什么方法可以完成上述工作？

Answer 1

让我们从头开始。如果您将WHERE表中的列与OUTER JOIN一起使用，则意味着您的查询：

SELECT DISTINCT c.*
FROM dbo.Collector_Capital_Equipment c
LEFT OUTER JOIN dbo.Lab_Space s ON c.Room = s.Entry_Bar_Code 
                                OR c.HomeRoom = s.Entry_Bar_Code
WHERE s.id = 1021645

在逻辑上等同于：

SELECT DISTINCT c.*
FROM dbo.Collector_Capital_Equipment c
JOIN dbo.Lab_Space s 
  ON c.Room = s.Entry_Bar_Code 
  OR c.HomeRoom = s.Entry_Bar_Code
WHERE s.id = 1021645;

这可以通过CROSS JOIN（伪代码）来实现：

var q = from c in Collector_Capital_Equipment
       from s in Lab_Space
       where s.id == 1021645 
          && (s.Entry_Bar_Code == c.Room || c.HomeRoom == s.Entry_Bar_Code)
       select ...

我假设您确实要生成查询：

SELECT DISTINCT c.*
FROM dbo.Collector_Capital_Equipment c
LEFT OUTER JOIN dbo.Lab_Space s 
  ON (c.Room = s.Entry_Bar_Code OR c.HomeRoom = s.Entry_Bar_Code)
  AND s.id = 1021645

可以表示为：

SELECT c.*
FROM dbo.Collector_Capital_Equipment c
LEFT OUTER JOIN dbo.Lab_Space s 
  ON c.Room = s.Entry_Bar_Code AND s.id = 1021645
INTERSECT
SELECT c.*
FROM dbo.Collector_Capital_Equipment c
LEFT OUTER JOIN dbo.Lab_Space s 
  ON c.HomeRoom = s.Entry_Bar_Code AND s.id = 1021645

以上查询可以使用LINQ使用集合运算符实现。

db<>fiddle demo

Answer 2

我认为我以前从未见过有人在联接上使用OR子句。 MS SQL Server甚至在SQL中支持吗？

说实话，我可能会将其分为两个查询。

SELECT entry_bar_code 
FROM dbo.Lab_Space WHERE id = 1021645;

将结果输入

SELECT DISTINCT * 
FROM dbo.Collector_Capital_Equipment 
WHERE c.room == <barcode> OR c.homeRoom == <barcode>

Linq to sql使用多个“或”过滤器联接

2 个答案: