[英]How to convert SQL subquery to Linq
I have two tables, Employees
and Transactions
.我有两个表, Employees
和Transactions
。
First table: dbo.Employees
第一个表: dbo.Employees
Second table: dbo.Transactions
第二个表: dbo.Transactions
I need to convert the below query to a lambda expression (Linq):我需要将以下查询转换为 lambda 表达式 (Linq):
SELECT Employees.EmployeeId, Trans.LastTrans
FROM dbo.Employees
INNER JOIN
(SELECT EmployeeId, MAX(TrasactionDate) LastTrans
FROM dbo.Transactions
GROUP BY EmployeeId) Trans ON Trans.EmployeeId = Employees.EmployeeId
I want the result employeeId
and LastTrans
as shown below:我想要的结果employeeId
和LastTrans
如下所示:
See following.见下文。 The query does not need two Select in linq :查询不需要 linq 中的两个 Select :
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
Context db = new Context()
{
Employees = new List<Employees>() {
new Employees() { EmployeeId = 1, Name = "Hossam"},
new Employees() { EmployeeId = 2, Name = "Peter"},
new Employees() { EmployeeId = 3, Name = "George"}
},
Transactions = new List<Transactions>() {
new Transactions() { TranactionId = 1, amount = 200, TransactionDate = DateTime.Parse("2020-01-02"), EmployeeId = 1},
new Transactions() { TranactionId = 2, amount = 300, TransactionDate = DateTime.Parse("2020-02-02"), EmployeeId = 1},
new Transactions() { TranactionId = 3, amount = 1000, TransactionDate = DateTime.Parse("2020-02-25"), EmployeeId = 1},
new Transactions() { TranactionId = 4, amount = 5000, TransactionDate = DateTime.Parse("2020-04-01"), EmployeeId = 2},
new Transactions() { TranactionId = 5, amount = 7000, TransactionDate = DateTime.Parse("2020-07-16"), EmployeeId = 2},
new Transactions() { TranactionId = 6, amount = 8000, TransactionDate = DateTime.Parse("2020-08-06"), EmployeeId = 3},
new Transactions() { TranactionId = 6, amount = 600, TransactionDate = DateTime.Parse("2020-09-04"), EmployeeId = 3}
}
};
var results = (from trans in db.Transactions
join emp in db.Employees on trans.EmployeeId equals emp.EmployeeId
select new { EmployeeId = trans.EmployeeId, LastTrans = trans.TransactionDate }
).GroupBy(x => x.EmployeeId)
.Select(x => x.OrderByDescending(y => y.LastTrans))
.Select(x => x.First())
.OrderBy(x => x.EmployeeId)
.ToList();
}
}
public class Context
{
public List<Employees> Employees { get; set; }
public List<Transactions> Transactions { get; set; }
}
public class Employees
{
public int EmployeeId { get; set; }
public string Name { get; set; }
}
public class Transactions
{
public int TranactionId { get; set; }
public decimal amount { get; set; }
public DateTime TransactionDate { get; set; }
public int EmployeeId { get; set; }
}
}
This query is enough to get your result and you do not need additional join to Employees此查询足以获得您的结果,您不需要额外加入员工
var grouped =
from trans in db.Transactions
group trans by trans.EmployeeId into g
select new
{
EmployeeId = g.Key,
LastTrans = g.Max(x => x.TrasactionDate)
};
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