SQL、Linq、lamda表达式同一功能不同写法

一、SQL、Linq、lamda表达式同一功能不同写法

SQL	LINQ	Lambda
SELECT * FROM HumanResources.Employee	from e in Employees select e	Employees .Select (e => e)
SELECT e.LoginID, e.JobTitle FROM HumanResources.Employee AS e	from e in Employees select new {e.LoginID, e.JobTitle}	Employees .Select ( e => new { LoginID = e.LoginID, JobTitle = e.JobTitle } )
SELECT e.LoginID AS ID, e.JobTitle AS Title FROM HumanResources.Employee AS e	from e in Employees select new {ID = e.LoginID, Title = e.JobTitle}	Employees .Select ( e => new { ID = e.LoginID, Title = e.JobTitle } )
SELECT DISTINCT e.JobTitle FROM HumanResources.Employee AS e	(from e in Employees select e.JobTitle).Distinct()	Employees .Select (e => e.JobTitle) .Distinct ()
SELECT e.* FROM HumanResources.Employee AS e WHERE e.LoginID = 'test'	from e in Employees where e.LoginID == "test" select e	Employees .Where (e => (e.LoginID == "test"))
SELECT e.* FROM HumanResources.Employee AS e WHERE e.LoginID = 'test' AND e.SalariedFlag = 1	from e in Employees where e.LoginID == "test" && e.SalariedFlag select e	Employees .Where (e => ((e.LoginID == "test") && e.SalariedFlag))
SELECT e.* FROM HumanResources.Employee AS e WHERE e.VacationHours >= 2 AND e.VacationHours <= 10	from e in Employees where e.VacationHours >= 2 && e.VacationHours <= 10 select e	Employees .Where (e => (((Int32)(e.VacationHours) >= 2) && ((Int32)(e.VacationHours) <= 10)))
SELECT e.* FROM HumanResources.Employee AS e ORDER BY e.NationalIDNumber	from e in Employees orderby e.NationalIDNumber select e	Employees .OrderBy (e => e.NationalIDNumber)
SELECT e.* FROM HumanResources.Employee AS e ORDER BY e.HireDate DESC, e.NationalIDNumber	from e in Employees orderby e.HireDate descending, e.NationalIDNumber select e	Employees .OrderByDescending (e => e.HireDate) .ThenBy (e => e.NationalIDNumber)
SELECT e.* FROM HumanResources.Employee AS e WHERE e.JobTitle LIKE 'Vice%' OR SUBSTRING(e.JobTitle, 0, 3) = 'Pro'	from e in Employees where e.JobTitle.StartsWith("Vice") \|\| e.JobTitle.Substring(0, 3) == "Pro" select e	Employees .Where (e => (e.JobTitle.StartsWith ("Vice") \|\| (e.JobTitle.Substring (0, 3) == "Pro")))
SELECT SUM(e.VacationHours) FROM HumanResources.Employee AS e		Employees.Sum(e => e.VacationHours);
SELECT COUNT(*) FROM HumanResources.Employee AS e		Employees.Count();
SELECT SUM(e.VacationHours) AS TotalVacations, e.JobTitle FROM HumanResources.Employee AS e GROUP BY e.JobTitle	from e in Employees group e by e.JobTitle into g select new {JobTitle = g.Key, TotalVacations = g.Sum(e => e.VacationHours)}	Employees .GroupBy (e => e.JobTitle) .Select ( g => new { JobTitle = g.Key, TotalVacations = g.Sum (e => (Int32)(e.VacationHours)) } )
SELECT e.JobTitle, SUM(e.VacationHours) AS TotalVacations FROM HumanResources.Employee AS e GROUP BY e.JobTitle HAVING e.COUNT(*) > 2	from e in Employees group e by e.JobTitle into g where g.Count() > 2 select new {JobTitle = g.Key, TotalVacations = g.Sum(e => e.VacationHours)}	Employees .GroupBy (e => e.JobTitle) .Where (g => (g.Count () > 2)) .Select ( g => new { JobTitle = g.Key, TotalVacations = g.Sum (e => (Int32)(e.VacationHours)) } )
SELECT * FROM Production.Product AS p, Production.ProductReview AS pr	from p in Products from pr in ProductReviews select new {p, pr}	Products .SelectMany ( p => ProductReviews, (p, pr) => new { p = p, pr = pr } )
SELECT * FROM Production.Product AS p INNER JOIN Production.ProductReview AS pr ON p.ProductID = pr.ProductID	from p in Products join pr in ProductReviews on p.ProductID equals pr.ProductID select new {p, pr}	Products .Join ( ProductReviews, p => p.ProductID, pr => pr.ProductID, (p, pr) => new { p = p, pr = pr } )
SELECT * FROM Production.Product AS p INNER JOIN Production.ProductCostHistory AS pch ON p.ProductID = pch.ProductID AND p.SellStartDate = pch.StartDate	from p in Products join pch in ProductCostHistories on new {p.ProductID, StartDate = p.SellStartDate} equals new {pch.ProductID, StartDate = pch.StartDate} select new {p, pch}	Products .Join ( ProductCostHistories, p => new { ProductID = p.ProductID, StartDate = p.SellStartDate }, pch => new { ProductID = pch.ProductID, StartDate = pch.StartDate }, (p, pch) => new { p = p, pch = pch } )
SELECT * FROM Production.Product AS p LEFT OUTER JOIN Production.ProductReview AS pr ON p.ProductID = pr.ProductID	from p in Products join pr in ProductReviews on p.ProductID equals pr.ProductID into prodrev select new {p, prodrev}	Products .GroupJoin ( ProductReviews, p => p.ProductID, pr => pr.ProductID, (p, prodrev) => new { p = p, prodrev = prodrev } )
SELECT p.ProductID AS ID FROM Production.Product AS p UNION SELECT pr.ProductReviewID FROM Production.ProductReview AS pr	(from p in Products select new {ID = p.ProductID}).Union( from pr in ProductReviews select new {ID = pr.ProductReviewID})	Products .Select ( p => new { ID = p.ProductID } ) .Union ( ProductReviews .Select ( pr => new { ID = pr.ProductReviewID } ) )
SELECT TOP (10) * FROM Production.Product AS p WHERE p.StandardCost < 100	(from p in Products where p.StandardCost < 100 select p).Take(10)	Products .Where (p => (p.StandardCost < 100)) .Take (10)
SELECT * FROM [Production].[Product] AS p WHERE p.ProductID IN( SELECT pr.ProductID FROM [Production].[ProductReview] AS [pr] WHERE pr.[Rating] = 5 )	from p in Products where (from pr in ProductReviews where pr.Rating == 5 select pr.ProductID).Contains(p.ProductID) select p	Products .Where ( p => ProductReviews .Where (pr => (pr.Rating == 5)) .Select (pr => pr.ProductID) .Contains (p.ProductID) )

SQL

LINQ

Lambda

SELECT *

FROM HumanResources.Employee

from e in Employees

select e

Employees
.Select (e => e)

SELECT e.LoginID, e.JobTitle

FROM HumanResources.Employee AS e

from e in Employees

select new {e.LoginID, e.JobTitle}

Employees
   .Select (
      e =>
         new
         {
            LoginID = e.LoginID,
            JobTitle = e.JobTitle
         }
   )

SELECT e.LoginID AS ID, e.JobTitle AS Title

FROM HumanResources.Employee AS e

from e in Employees

select new {ID = e.LoginID, Title = e.JobTitle}

Employees
   .Select (
      e =>
         new
         {
            ID = e.LoginID,
            Title = e.JobTitle
         }
   )

SELECT DISTINCT e.JobTitle

FROM HumanResources.Employee AS e

(from e in Employees

select e.JobTitle).Distinct()

Employees
.Select (e => e.JobTitle)
.Distinct ()

SELECT e.*

FROM HumanResources.Employee AS e

WHERE e.LoginID = 'test'

from e in Employees

where e.LoginID == "test"

select e

Employees
.Where (e => (e.LoginID == "test"))

SELECT e.*

FROM HumanResources.Employee AS e

WHERE e.LoginID = 'test' AND e.SalariedFlag = 1

from e in Employees

where e.LoginID == "test" && e.SalariedFlag

select e

Employees
.Where (e => ((e.LoginID == "test") && e.SalariedFlag))

SELECT e.*
FROM HumanResources.Employee AS e

WHERE e.VacationHours >= 2 AND e.VacationHours <= 10

from e in Employees

where e.VacationHours >= 2 && e.VacationHours <= 10

select e

Employees
.Where (e => (((Int32)(e.VacationHours) >= 2) && ((Int32)(e.VacationHours) <= 10)))

SELECT e.*

FROM HumanResources.Employee AS e
ORDER BY e.NationalIDNumber

from e in Employees

orderby e.NationalIDNumber

select e

Employees
.OrderBy (e => e.NationalIDNumber)

SELECT e.*

FROM HumanResources.Employee AS e

ORDER BY e.HireDate DESC, e.NationalIDNumber

from e in Employees

orderby e.HireDate descending, e.NationalIDNumber

select e

Employees
.OrderByDescending (e => e.HireDate)
.ThenBy (e => e.NationalIDNumber)

SELECT e.*
FROM HumanResources.Employee AS e

WHERE e.JobTitle LIKE 'Vice%' OR SUBSTRING(e.JobTitle, 0, 3) = 'Pro'

from e in Employees

where e.JobTitle.StartsWith("Vice") || e.JobTitle.Substring(0, 3) == "Pro"

select e

Employees
.Where (e => (e.JobTitle.StartsWith ("Vice") || (e.JobTitle.Substring (0, 3) == "Pro")))

SELECT SUM(e.VacationHours)

FROM HumanResources.Employee AS e

Employees.Sum(e => e.VacationHours);

SELECT COUNT(*)

FROM HumanResources.Employee AS e

Employees.Count();

SELECT SUM(e.VacationHours) AS TotalVacations, e.JobTitle

FROM HumanResources.Employee AS e

GROUP BY e.JobTitle

from e in Employees

group e by e.JobTitle into g

select new {JobTitle = g.Key, TotalVacations = g.Sum(e => e.VacationHours)}

Employees
   .GroupBy (e => e.JobTitle)
   .Select (
      g =>
         new
         {
            JobTitle = g.Key,
            TotalVacations = g.Sum (e => (Int32)(e.VacationHours))
         }
   )

SELECT e.JobTitle, SUM(e.VacationHours) AS TotalVacations

FROM HumanResources.Employee AS e

GROUP BY e.JobTitle

HAVING e.COUNT(*) > 2

from e in Employees

group e by e.JobTitle into g

where g.Count() > 2

select new {JobTitle = g.Key, TotalVacations = g.Sum(e => e.VacationHours)}

Employees
   .GroupBy (e => e.JobTitle)
   .Where (g => (g.Count () > 2))
   .Select (
      g =>
         new
         {
            JobTitle = g.Key,
            TotalVacations = g.Sum (e => (Int32)(e.VacationHours))
         }
   )

SELECT *

FROM Production.Product AS p, Production.ProductReview AS pr

from p in Products

from pr in ProductReviews

select new {p, pr}

Products
   .SelectMany (
      p => ProductReviews,
      (p, pr) =>
         new
         {
            p = p,
            pr = pr
         }
   )

SELECT *

FROM Production.Product AS p

INNER JOIN Production.ProductReview AS pr ON p.ProductID = pr.ProductID

from p in Products

join pr in ProductReviews on p.ProductID equals pr.ProductID

select new {p, pr}

Products
   .Join (
      ProductReviews,
      p => p.ProductID,
      pr => pr.ProductID,
      (p, pr) =>
         new
         {
            p = p,
            pr = pr
         }
   )

SELECT *

FROM Production.Product AS p

INNER JOIN Production.ProductCostHistory AS pch ON p.ProductID = pch.ProductID AND p.SellStartDate = pch.StartDate

from p in Products

join pch in ProductCostHistories on new {p.ProductID, StartDate = p.SellStartDate} equals new {pch.ProductID, StartDate = pch.StartDate}

select new {p, pch}

Products
   .Join (
      ProductCostHistories,
      p =>
         new
         {
            ProductID = p.ProductID,
            StartDate = p.SellStartDate
         },
      pch =>
         new
         {
            ProductID = pch.ProductID,
            StartDate = pch.StartDate
         },
      (p, pch) =>
         new
         {
            p = p,
            pch = pch
         }
   )

SELECT *

FROM Production.Product AS p

LEFT OUTER JOIN Production.ProductReview AS pr ON p.ProductID = pr.ProductID

from p in Products

join pr in ProductReviews on p.ProductID equals pr.ProductID

into prodrev

select new {p, prodrev}

Products
   .GroupJoin (
      ProductReviews,
      p => p.ProductID,
      pr => pr.ProductID,
      (p, prodrev) =>
         new
         {
            p = p,
            prodrev = prodrev
         }
   )

SELECT p.ProductID AS ID

FROM Production.Product AS p

UNION

SELECT pr.ProductReviewID

FROM Production.ProductReview AS pr

(from p in Products

select new {ID = p.ProductID}).Union(

from pr in ProductReviews

select new {ID = pr.ProductReviewID})

Products
   .Select (
      p =>
         new
         {
            ID = p.ProductID
         }
   )
   .Union (
      ProductReviews
         .Select (
            pr =>
               new
               {
                  ID = pr.ProductReviewID
               }
         )
   )

SELECT TOP (10) *

FROM Production.Product AS p

WHERE p.StandardCost < 100

(from p in Products

where p.StandardCost < 100

select p).Take(10)

Products
.Where (p => (p.StandardCost < 100))
.Take (10)

SELECT *

FROM [Production].[Product] AS p

WHERE p.ProductID IN(

SELECT pr.ProductID

FROM [Production].[ProductReview] AS [pr]

WHERE pr.[Rating] = 5

)

from p in Products

where (from pr in ProductReviews

where pr.Rating == 5

select pr.ProductID).Contains(p.ProductID)

select p

Products
   .Where (
      p =>
         ProductReviews
            .Where (pr => (pr.Rating == 5))
            .Select (pr => pr.ProductID)
            .Contains (p.ProductID)
   )

二、同一功能的几种不同写法的实例

1、简单的函数计算（count，min，max，sum）

C# 代码复制

//1

            ////获取最大的rpId

            var ss = (from r in db.Am_recProScheme

                      select r).Max(p => p.rpId);

            ////获取最小的rpId

            var ss = (from r in db.Am_recProScheme

                      select r).Min(p => p.rpId);

            //获取结果集的总数

              var ss = (from r in db.Am_recProScheme

                     select r).Count();

            //获取rpId的和

            var ss = (from r in db.Am_recProScheme

                      select r).Sum(p => p.rpId);





            //2

            var ss1 = db.Am_recProScheme.Max(p=>p.rpId);

            var ss1 = db.Am_recProScheme.Min(p => p.rpId);

            var ss1 = db.Am_recProScheme.Count() ;

            var ss1 = db.Am_recProScheme.Sum(p => p.rpId);

            Response.Write(ss);



            //3

            string sssql = "select max(rpId) from Am_recProScheme";

            sssql = "select min(rpId) from Am_recProScheme";

            sssql = "select count(1) from Am_recProScheme";

            sssql = "select sum(rpId) from Am_recProScheme";

2、排序order by desc/asc

C# 代码复制

          var ss = from r in db.Am_recProScheme

                     where r.rpId > 10

                     orderby r.rpId descending  //倒序

                     //  orderby r.rpId ascending   //正序

                     select r;

          //正序

           var ss1 = db.Am_recProScheme.OrderBy(p => p.rpId).Where(p => p.rpId > 10).ToList();

          //倒序

           var ss2 = db.Am_recProScheme.OrderByDescending(p => p.rpId).Where(p => p.rpId > 10).ToList();

          string sssql = "select * from Am_recProScheme where rpid>10 order by rpId [desc|asc]";

3、top

C# 代码复制

//1

          //如果取最后一个可以按倒叙排列再取值

           var ss = (from r in db.Am_recProScheme select r).FirstOrDefault();

//2

          string sssql = "select top(1) * from Am_recProScheme";

4、跳过前面多少条数据取余下的数据

C# 代码复制

//1

           var ss = (from r in db.Am_recProScheme

                      orderby r.rpId descending

                      select r).Skip(10); //跳过前10条数据，取10条之后的所有数据

//2

           var ss1 = db.Am_recProScheme.OrderByDescending(p => p.rpId).Skip(10).ToList();

//3

           string sssql = "select * from  (select ROW_NUMBER()over(order by rpId desc) as rowNum, * from [Am_recProScheme]) as t where rowNum>10";

5、分页数据查询

C# 代码复制

//1

           var ss = (from r in db.Am_recProScheme

                      where r.rpId > 10

                      orderby r.rpId descending

                      select r).Skip(10).Take(10); //取第11条到第20条数据

            //2 Take(10): 数据从开始获取，获取指定数量（10）的连续数据

            var ss1 = db.Am_recProScheme.OrderByDescending(p => p.rpId).Where(p => p.rpId > 10).Skip(10).Take(10).ToList();

//3

           string sssql = "select * from  (select ROW_NUMBER()over(order by rpId desc) as rowNum, * from [Am_recProScheme]) as t where rowNum>10 and rowNum<=20";

6、包含，类似like '%%'

C# 代码复制

//1

            var ss = from r in db.Am_recProScheme

                     where r.SortsText.Contains("张")

                     select r;

//2

            var ss1 = db.Am_recProScheme.Where(p => p.SortsText.Contains("张")).ToList();

//3

            string sssql = "select * from Am_recProScheme where SortsText like '%张%'";

7、分组group by

C# 代码复制

//1

            var ss = from r in db.Am_recProScheme

                     orderby r.rpId descending

                     group r by r.recType into n

                     select new

                     {

                         n.Key,  //这个Key是recType

                         rpId = n.Sum(r => r.rpId), //组内rpId之和

                         MaxRpId = n.Max(r => r.rpId),//组内最大rpId

                         MinRpId = n.Min(r => r.rpId), //组内最小rpId

                     };

            foreach (var t in ss)

            {

                Response.Write(t.Key + "--" + t.rpId + "--" + t.MaxRpId + "--" + t.MinRpId);

            }



            //2

            var ss1 = from r in db.Am_recProScheme

                     orderby r.rpId descending

                     group r by r.recType into n

                     select n;

            foreach (var t in ss1)

            {

                Response.Write(t.Key + "--" + t.Min(p => p.rpId));

            }



            //3

            var ss2 = db.Am_recProScheme.GroupBy(p => p.recType);

            foreach (var t in ss2)

            {

                Response.Write(t.Key + "--" + t.Min(p => p.rpId));

            }



            //4

            string sssql = "select recType,min(rpId),max(rpId),sum(rpId) from Am_recProScheme group by recType";

8、连接查询

C# 代码复制

//1

            var ss = from r in db.Am_recProScheme

                     join w in db.Am_Test_Result on r.rpId equals w.rsId

                     orderby r.rpId descending

                     select r;

//2

            var ss1 = db.Am_recProScheme.Join(db.Am_Test_Result, p => p.rpId, r => r.rsId, (p, r) => p).OrderByDescending(p => p.rpId).ToList();

//3

            string sssql = "select r.* from  [Am_recProScheme] as r inner join [dbo].[Am_Test_Result] as t on r.[rpId] = t.[rsId] order by r.[rpId] desc";

9、sql中的In

C# 代码复制

//1

            var ss = from p in db.Am_recProScheme

                              where (new int?[] { 24, 25,26 }).Contains(p.rpId)

                              select p;

            foreach (var p in ss)

            {

                Response.Write(p.Sorts);

            }



            //2

            string st = "select * from Am_recProScheme where rpId in(24,25,26)";

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