LINQ to SQL：如何實現最少或類似的功能？

Question

考慮：

命名TABLE_1與下列的表：

• ID
• ColumnA
• ColumnB
• ColumnC
• ColumnD

我有SQL查詢，其中TABLE_1根據ColumnA，ColumnB，ColumnC加入本身兩次。該查詢可能是這個樣子：

Select t1.ID, t2.ID, t3.ID, LEAST(t1.ColumnD, t2.ColumnD, t3.ColumnD) 
    From TABLE_1 t1 
    Left Join TABLE_1 t2 On 
     t1.ColumnA = t2.ColumnA 
    And t1.ColumnB = t2.ColumnB 
    And t1.ColumnC = t2.ColumnC 
    Left Join TABLE_1 t3 On 
     t2.ColumnA = t3.ColumnA 
    And t2.ColumnB = t3.ColumnB 
    And t2.ColumnC = t3.ColumnC 

問題：

我需要查詢的LINQ被重寫。我嘗試了一下：

var query = 
    from t1 in myTABLE1List // List<TABLE_1> 
    join t2 in myTABLE1List 
     on new {t1.ColumnA, t1.ColumnB, t2.ColumnC} 
    equals new {t2.ColumnA, t2.ColumnB, t2.ColumnC} 
    join t3 in myTABLE1List 
     on new {t2.ColumnA, t2.ColumnB, t2.ColumnC} 
    equals new {t3.ColumnA, t3.ColumnB, t3.ColumnC} 
    select new { 
    ID_1 = s1.ID, 
    ID_2 = s2.ID, 
    ID_3 = s3.ID, 
    // Invalid anonymous type member declarator. 
    // Anonymous type members must be declared with a member assignment, 
    // simple name or member access. 
    // how can I implement this? 
    least(s1.ColumnD, s2.ColumnD, s3.ColumnD) 
    }; 

.... 

private object least(params object[] objects) 
{ 
    // code here that sorts the objects and returns the 'smallest' of them. 

    return leastObject; 
} 

如何在LINQ中編寫我的查詢？我究竟做錯了什麼？我認爲可以在LINQ表達式中使用函數，那麼爲什麼我會得到這個錯誤？

Answer 1

我可能是錯的，但我認爲你需要的least結果分配到新的匿名類型實例的實際成員，如：

select new { 
    ID_1 = s1.ID, 
    ID_2 = s2.ID, 
    ID_3 = s3.ID, 
    Least = least(s1.ColumnD, s2.ColumnD, s3.ColumnD) 
}; 

Answer 2

怎麼樣？

MinOfColumnD = Math.Min(Math.Min(s1.ColumnD, s2.ColumnD), s3.ColumnD)) 

編輯：假設ColumnD在每個表中的數字是&「least`（在這種情況下）是在給定的列3號的最小值。

編輯：如果列是字符串，確定什麼最大。它可以容納的值&對它做一個.Parse。 例如

MinOfColumnD = Math.Min(Math.Min(int.Parse(s1.ColumnD), int.Parse(s2.ColumnD)), int.Parse(s3.ColumnD)))