如何将sql查询转换为linq查询

Posted 2023-03-23

【中文标题】如何将sql查询转换为linq查询

【英文标题】：How to transform sql query to linq query

【发布时间】：2013-06-12 11:33:12

【问题描述】：

delete  from detail where autoid not in (select min(autoid) from detail
where CATEGORY<>'Accepted'
group by ATM_Id, Date, Card ,Transit ,Ck)
and CATEGORY<>'Accepted'

我的尝试

     var Query2 = from line in
     (from line in source let fields = line.Split(',')
     select new   autoid = fields[0],
          ATMID = fields[4],
          DATE = fields[2],
          CARDNo = fields[5],
          TRANSIT = fields[8],
          CheckNo = fields[9],
          CATEGORY = fields[10],
      )
      orderby line.ATMID, 
              line.DATE, 
              line.CARDNo, 
              line.TRANSIT, 
              line.CheckNo ascending
      where   line.CATEGORY != "Accepted"
      group line by new    line.ATMID,
                            line.DATE, 
                            line.CARDNo, 
                            line.TRANSIT, 
                            line.CheckNo  
      into gruoped
      where gruoped.Count() > 1

                 //select autoid = gruoped.Key;
      select new
      
                     //ATMID = gruoped.Key,
                     //DATE = gruoped.Key,
                     //CARDNo = gruoped.Key,
                     //TRANSIT = gruoped.Key,
                     //CheckNo = gruoped.Key,
                     autoid = gruoped.Key,
                     //CATEGORY = gruoped.Key
      ;

【参考方案1】：

这是一个示例，它应该如何工作，看看这个

var remove = (from aremove in db.logins 
             where aremove.username == userNameString 
                && aremove.Password == pwdString 
             select aremove).FirstOrDefault(); 

if(remove != null)

    db.logins.DeleteOnSubmit(remove);

如果您有任何问题，请随时提问！

【讨论】：

好的..但是我没有使用数据库，我的详细数据库是一个逗号分隔的文本文件，我需要从中删除重复的行...是否可以删除重复的行...谢谢

@user2448680 你应该试试你自己..如果你有问题问一个问题

【参考方案2】：

你可以试试这个。

var ids = (from d in detail
where d.Category != "Accepted"
group d by new d.ATM_Id, d.Date, d.Card ,d.Transit ,d.Ck into grp
select  grp.Min(x => x.autoId));


var toDelete = (from d in detail
            where !ids.Contains(d.AutoId) && d.Category != "Accepted"
            select d);

context.DeleteOnSubmit(toDelete);   

您可以只搜索所需的内容，然后重新创建逗号分隔字符串的新列表以存储回文件。

EG：

void Main()


    var fields = new List<Field>
        new FieldId = 1, Name = "A",
        new FieldId = 1, Name = "A",
        new FieldId = 2, Name = "B",
        new FieldId = 1, Name = "A",
        new FieldId = 3, Name = "C",
        new FieldId = 2, Name = "B",
    ;

    // Grouped 
    var grouped = (from f in fields
                group f by new f.Id, f.Name into grp
                select new Field
                
                        Id = grp.Select(x => x.Id).FirstOrDefault(),
                        Name = grp.Select(x => x.Name).FirstOrDefault()
                
                );

    // Makes a list of the distinct Fields             
    var list_Of_CSV_Items = grouped.Select(x => string.Join(",", x.Id,x.Name));

    System.IO.File.WriteAllLines(@"C:\Where_your_folder_is.txt", list_Of_CSV_Items);


public class Field

    public int Id get;set;
    public string Name get; set;
         

【讨论】：

context.DeleteOnSubmit(toDelete);在这个语句给出一些错误之后......查询正文必须以 select 或 group 子句结尾..

抱歉看到编辑，刚刚添加了select d。我使用文本编辑器来执行此操作。上下文也是您的 DataContext 所以将它交换为您的 DataContext 实例的名称。

好的..但是我没有使用DataContext，我的详细数据库是一个逗号分隔的文本文件，我需要从中删除重复的行...是否可以删除重复的行...谢谢..

添加了一些内容供您试用并应用于您的代码。它采用独特的项目并创建一个新的逗号分隔字符串列表，供您存储回您的文件或其他内容。

谢谢我明白了......但下一个问题是，我有一个文本文件有超过 2(2000000) 行缺少行，所以它没有产生结果..但它的工作量高达 1000行...