Linq to sql查询句法
select
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描述：查詢顧客的公司名、地址信息
查詢句法：
| var 構建匿名類型1 = from c in ctx.Customers ????????????????????? select new ????????????????????? { ????????????????????????? 公司名 = c.CompanyName, ????????????????????????? 地址 = c.Address ????????????????????? }; |
對應SQL：
| SELECT [t0].[CompanyName], [t0].[Address] FROM [dbo].[Customers] AS [t0]?????? |
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描述：查詢職員的姓名和雇用年份
查詢句法：
| var 構建匿名類型2 = from emp in ctx.Employees ????????????????????? select new ????????????????????? { ????????????????????????? 姓名 = emp.LastName + emp.FirstName, ?????????????????????????雇用年 = emp.HireDate.Value.Year ????????????????????? }; |
對應SQL：
| SELECT [t0].[LastName] + [t0].[FirstName] AS [value], DATEPART(Year, [t0].[HireDate]) AS [value2] FROM [dbo].[Employees] AS [t0] |
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描述：查詢顧客的ID以及聯系信息（職位和聯系人）
查詢句法：
| var 構建匿名類型3 = from c in ctx.Customers ????????????????????? select new ????????????????????? { ????????????????????????? ID = c.CustomerID, ????????????????????????? 聯系信息 = new ????????????????????????? { ????????????????????????????? 職位 = c.ContactTitle, ?????? ???????????????????????聯系人 = c.ContactName ????????????????????????? } ????????????????????? }; |
對應SQL：
| SELECT [t0].[CustomerID], [t0].[ContactTitle], [t0].[ContactName] FROM [dbo].[Customers] AS [t0] |
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描述：查詢訂單號和訂單是否超重的信息
查詢句法：
| var select帶條件 = from o in ctx.Orders ??????????????????????? select new ??????????????????????? { ??????????????????????????? 訂單號 = o.OrderID, ??????????????????????????? 是否超重 = o.Freight > 100 ? "是" : "否" ??????????????????????? }; |
對應SQL：
| SELECT [t0].[OrderID], ??? (CASE ??????? WHEN [t0].[Freight] > @p0 THEN @p1 ??????? ELSE @p2 ???? END) AS [value] FROM [dbo].[Orders] AS [t0] -- @p0: Input Currency (Size = 0; Prec = 19; Scale = 4) [100] -- @p1: Input String (Size = 1; Prec = 0; Scale = 0) [是] -- @p2: Input String (Size = 1; Prec = 0; Scale = 0) [否] |
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where
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描述：查詢顧客的國家、城市和訂單數信息，要求國家是法國并且訂單數大于5
查詢句法：
| var 多條件 = from c in ctx.Customers ????????????????? where c.Country == "France" && c.Orders.Count > 5 ????????????????? select new ????????????????? { ????????????????????? 國家 = c.Country, ????????????????????? 城市 = c.City, ????????????????????? 訂單數 = c.Orders.Count ????????????????? };?????? |
對應SQL：
| SELECT [t0].[Country], [t0].[City], ( ??? SELECT COUNT(*) ??? FROM [dbo].[Orders] AS [t2] ??? WHERE [t2].[CustomerID] = [t0].[CustomerID] ??? ) AS [value] FROM [dbo].[Customers] AS [t0] WHERE ([t0].[Country] = @p0) AND ((( ??? SELECT COUNT(*) ??? FROM [dbo].[Orders] AS [t1] ??? WHERE [t1].[CustomerID] = [t0].[CustomerID] ??? )) > @p1) -- @p0: Input String (Size = 6; Prec = 0; Scale = 0) [France] -- @p1: Input Int32 (Size = 0; Prec = 0; Scale = 0) [5]???? |
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orderby
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描述：查詢所有沒有下屬雇員的雇用年和名，按照雇用年倒序，按照名正序
查詢句法：
| ?var 排序 = from emp in ctx.Employees ???????????????? where emp.Employees.Count == 0 ???????????????? orderby emp.HireDate.Value.Year descending, emp.FirstName ascending ???????????????? select new ???????????????? { ???????????????????? 雇用年 = emp.HireDate.Value.Year, ???????????????????? 名 = emp.FirstName ???????????????? };????? |
對應SQL：
| SELECT DATEPART(Year, [t0].[HireDate]) AS [value], [t0].[FirstName] FROM [dbo].[Employees] AS [t0] WHERE (( ??? SELECT COUNT(*) ???FROM [dbo].[Employees] AS [t1] ??? WHERE [t1].[ReportsTo] = [t0].[EmployeeID] ??? )) = @p0 ORDER BY DATEPART(Year, [t0].[HireDate]) DESC, [t0].[FirstName] -- @p0: Input Int32 (Size = 0; Prec = 0; Scale = 0) [0] |
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分頁
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描述：按照每頁10條記錄，查詢第二頁的顧客
查詢句法：
| ?var 分頁 = (from c in ctx.Customers select c).Skip(10).Take(10); |
對應SQL：
| SELECT TOP 10 [t1].[CustomerID], [t1].[CompanyName], [t1].[ContactName], [t1].[ContactTitle], [t1].[Address], [t1].[City], [t1].[Region], [t1].[PostalCode], [t1].[Country], [t1].[Phone], [t1].[Fax] FROM ( ??? SELECT ROW_NUMBER() OVER (ORDER BY [t0].[CustomerID], [t0].[CompanyName], [t0].[ContactName], [t0].[ContactTitle], [t0].[Address], [t0].[City], [t0].[Region], [t0].[PostalCode], [t0].[Country], [t0].[Phone], [t0].[Fax]) AS [ROW_NUMBER], [t0].[CustomerID], [t0].[CompanyName], [t0].[ContactName], [t0].[ContactTitle], [t0].[Address], [t0].[City], [t0].[Region], [t0].[PostalCode], [t0].[Country], [t0].[Phone], [t0].[Fax] ??? FROM [dbo].[Customers] AS [t0] ??? ) AS [t1] WHERE [t1].[ROW_NUMBER] > @p0 -- @p0: Input Int32 (Size = 0; Prec = 0; Scale = 0) [10] |
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分組
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描述：根據顧客的國家分組，查詢顧客數大于5的國家名和顧客數
查詢句法：
| ??????? var 一般分組 = from c in ctx.Customers ?????????????????? group c by c.Country into g ?????????????????? where g.Count() > 5 ?????????????????? orderby g.Count() descending ?????????????????? select new ?????????????????? { ?????????????????????? 國家 = g.Key, ?????????????????????? 顧客數 = g.Count() ?????????????????? }; |
對應SQL：
| SELECT [t1].[Country], [t1].[value3] AS [顧客數] FROM ( ??? SELECT COUNT(*) AS [value], COUNT(*) AS [value2], COUNT(*) AS [value3], [t0].[Country] ??? FROM [dbo].[Customers] AS [t0] ??? GROUP BY [t0].[Country] ??? ) AS [t1] WHERE [t1].[value] > @p0 ORDER BY [t1].[value2] DESC -- @p0: Input Int32 (Size = 0; Prec = 0; Scale = 0) [5] |
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描述：根據國家和城市分組，查詢顧客覆蓋的國家和城市
查詢句法：
| ???? var 匿名類型分組 = from c in ctx.Customers ???????????????????? group c by new { c.City, c.Country } into g ???????????????????? orderby g.Key.Country, g.Key.City ???????????????????? select new ???????????????????? { ?????? ??????????????????國家 = g.Key.Country, ???????????????????????? 城市 = g.Key.City ???????????????????? }; |
對應SQL：
| SELECT [t1].[Country], [t1].[City] FROM ( ??? SELECT [t0].[City], [t0].[Country] ??? FROM [dbo].[Customers] AS [t0] ??? GROUP BY [t0].[City], [t0].[Country] ??? ) AS [t1] ORDER BY [t1].[Country], [t1].[City] |
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描述：按照是否超重條件分組，分別查詢訂單數量
查詢句法：
| var 按照條件分組 = from o in ctx.Orders ???????????????????? group o by new { 條件 = o.Freight > 100 } into g ???????????????????? select new ???????????????????? { ???? ????????????????????數量 = g.Count(), ???????????????????????? 是否超重 = g.Key.條件 ? "是" : "否" ???????????????????? }; |
對應SQL：
| SELECT ??? (CASE ??????? WHEN [t2].[value2] = 1 THEN @p1 ??????? ELSE @p2 ???? END) AS [value], [t2].[value] AS [數量] FROM ( ??? SELECT COUNT(*) AS [value], [t1].[value] AS [value2] ??? FROM ( ??????? SELECT ??????????? (CASE ??????????????? WHEN [t0].[Freight] > @p0 THEN 1 ??????????????? WHEN NOT ([t0].[Freight] > @p0) THEN 0 ??????????????? ELSE NULL ???????????? END) AS [value] ?? ?????FROM [dbo].[Orders] AS [t0] ??????? ) AS [t1] ??? GROUP BY [t1].[value] ??? ) AS [t2] -- @p0: Input Currency (Size = 0; Prec = 19; Scale = 4) [100] -- @p1: Input String (Size = 1; Prec = 0; Scale = 0) [是] -- @p2: Input String (Size = 1; Prec = 0; Scale = 0) [否] |
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distinct
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描述：查詢顧客覆蓋的國家
查詢句法：
| var 過濾相同項 = (from c in ctx.Customers orderby c.Country select c.Country).Distinct(); |
對應SQL：
| SELECT DISTINCT [t0].[Country] FROM [dbo].[Customers] AS [t0] |
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union
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描述：查詢城市是A打頭和城市包含A的顧客并按照顧客名字排序
查詢句法：
| var 連接并且過濾相同項 = (from c in ctx.Customers where c.City.Contains("A") select c).Union ??????????? (from c in ctx.Customers where c.ContactName.StartsWith("A") select c).OrderBy(c => c.ContactName); |
對應SQL：
| SELECT [t3].[CustomerID], [t3].[CompanyName], [t3].[ContactName], [t3].[ContactTitle], [t3].[Address], [t3].[City], [t3].[Region], [t3].[PostalCode], [t3].[Country], [t3].[Phone], [t3].[Fax] FROM ( ??? SELECT [t2].[CustomerID], [t2].[CompanyName], [t2].[ContactName], [t2].[ContactTitle], [t2].[Address], [t2].[City], [t2].[Region], [t2].[PostalCode], [t2].[Country], [t2].[Phone], [t2].[Fax] ??? FROM ( ??????? SELECT [t0].[CustomerID], [t0].[CompanyName], [t0].[ContactName], [t0].[ContactTitle], [t0].[Address], [t0].[City], [t0].[Region], [t0].[PostalCode], [t0].[Country], [t0].[Phone], [t0].[Fax] ??????? FROM [dbo].[Customers] AS [t0] ??????? WHERE [t0].[City] LIKE @p0 ??????? UNION ??????? SELECT [t1].[CustomerID], [t1].[CompanyName], [t1].[ContactName], [t1].[ContactTitle], [t1].[Address], [t1].[City], [t1].[Region], [t1].[PostalCode], [t1].[Country], [t1].[Phone], [t1].[Fax] ??????? FROM [dbo].[Customers] AS [t1] ??????? WHERE [t1].[ContactName] LIKE @p1 ??????? ) AS [t2] ??? ) AS [t3] ORDER BY [t3].[ContactName] -- @p0: Input String (Size = 3; Prec = 0; Scale = 0) [%A%] -- @p1: Input String (Size = 2; Prec = 0; Scale = 0) [A%] |
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concat
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描述：查詢城市是A打頭和城市包含A的顧客并按照顧客名字排序，相同的顧客信息不會過濾
查詢句法：
| var 連接并且不過濾相同項 = (from c in ctx.Customers where c.City.Contains("A") select c).Concat ??????????? (from c in ctx.Customers where c.ContactName.StartsWith("A") select c).OrderBy(c => c.ContactName); |
對應SQL：
| SELECT [t3].[CustomerID], [t3].[CompanyName], [t3].[ContactName], [t3].[ContactTitle], [t3].[Address], [t3].[City], [t3].[Region], [t3].[PostalCode], [t3].[Country], [t3].[Phone], [t3].[Fax] FROM ( ??? SELECT [t2].[CustomerID], [t2].[CompanyName], [t2].[ContactName], [t2].[ContactTitle], [t2].[Address], [t2].[City], [t2].[Region], [t2].[PostalCode], [t2].[Country], [t2].[Phone], [t2].[Fax] ??? FROM ( ??????? SELECT [t0].[CustomerID], [t0].[CompanyName], [t0].[ContactName], [t0].[ContactTitle], [t0].[Address], [t0].[City], [t0].[Region], [t0].[PostalCode], [t0].[Country], [t0].[Phone], [t0].[Fax] ??????? FROM [dbo].[Customers] AS [t0] ??????? WHERE [t0].[City] LIKE @p0 ??????? UNION ALL ??????? SELECT [t1].[CustomerID], [t1].[CompanyName], [t1].[ContactName], [t1].[ContactTitle], [t1].[Address], [t1].[City], [t1].[Region], [t1].[PostalCode], [t1].[Country], [t1].[Phone], [t1].[Fax] ??????? FROM [dbo].[Customers] AS [t1] ??????? WHERE [t1].[ContactName] LIKE @p1 ??????? ) AS [t2] ??? ) AS [t3] ORDER BY [t3].[ContactName] -- @p0: Input String (Size = 3; Prec = 0; Scale = 0) [%A%] -- @p1: Input String (Size = 2; Prec = 0; Scale = 0) [A%] |
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取相交項
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描述：查詢城市是A打頭的顧客和城市包含A的顧客的交集，并按照顧客名字排序
查詢句法：
| var 取相交項 = (from c in ctx.Customers where c.City.Contains("A") select c).Intersect ??????????? (from c in ctx.Customers where c.ContactName.StartsWith("A") select c).OrderBy(c => c.ContactName); |
對應SQL：
| SELECT [t1].[CustomerID], [t1].[CompanyName], [t1].[ContactName], [t1].[ContactTitle], [t1].[Address], [t1].[City], [t1].[Region], [t1].[PostalCode], [t1].[Country], [t1].[Phone], [t1].[Fax] FROM ( ??? SELECT DISTINCT [t0].[CustomerID], [t0].[CompanyName], [t0].[ContactName], [t0].[ContactTitle], [t0].[Address], [t0].[City], [t0].[Region], [t0].[PostalCode], [t0].[Country], [t0].[Phone], [t0].[Fax] ??? FROM [dbo].[Customers] AS [t0] ??? ) AS [t1] WHERE (EXISTS( ??? SELECT NULL AS [EMPTY] ??? FROM [dbo].[Customers] AS [t2] ??? WHERE ([t1].[CustomerID] = [t2].[CustomerID]) AND ([t2].[ContactName] LIKE @p0) ??? )) AND ([t1].[City] LIKE @p1) ORDER BY [t1].[ContactName] -- @p0: Input String (Size = 2; Prec = 0; Scale = 0) [A%] -- @p1: Input String (Size = 3; Prec = 0; Scale = 0) [%A%] |
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排除相交項
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描述：查詢城市包含A的顧客并從中刪除城市以A開頭的顧客，并按照顧客名字排序
查詢句法：
| var 排除相交項 = (from c in ctx.Customers where c.City.Contains("A") select c).Except ??????????? (from c in ctx.Customers where c.ContactName.StartsWith("A") select c).OrderBy(c => c.ContactName); |
對應SQL：
| SELECT [t1].[CustomerID], [t1].[CompanyName], [t1].[ContactName], [t1].[ContactTitle], [t1].[Address], [t1].[City], [t1].[Region], [t1].[PostalCode], [t1].[Country], [t1].[Phone], [t1].[Fax] FROM ( ??? SELECT DISTINCT [t0].[CustomerID], [t0].[CompanyName], [t0].[ContactName], [t0].[ContactTitle], [t0].[Address], [t0].[City], [t0].[Region], [t0].[PostalCode], [t0].[Country], [t0].[Phone], [t0].[Fax] ??? FROM [dbo].[Customers] AS [t0] ??? ) AS [t1] WHERE (NOT (EXISTS( ??? SELECT NULL AS [EMPTY] ??? FROM [dbo].[Customers] AS [t2] ??? WHERE ([t1].[CustomerID] = [t2].[CustomerID]) AND ([t2].[ContactName] LIKE @p0) ?? ?))) AND ([t1].[City] LIKE @p1) ORDER BY [t1].[ContactName] -- @p0: Input String (Size = 2; Prec = 0; Scale = 0) [A%] -- @p1: Input String (Size = 3; Prec = 0; Scale = 0) [%A%] |
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子查詢
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描述：查詢訂單數超過5的顧客信息
查詢句法：
| var?子查詢 = from c in ctx.Customers ????????????? ?????where ?????????????????????? (from o in ctx.Orders group o by o.CustomerID into o where o.Count() > 5 select o.Key).Contains(c.CustomerID) ?????????????????? select c; |
對應SQL：
| SELECT [t0].[CustomerID], [t0].[CompanyName], [t0].[ContactName], [t0].[ContactTitle], [t0].[Address], [t0].[City], [t0].[Region], [t0].[PostalCode], [t0].[Country], [t0].[Phone], [t0].[Fax] FROM [dbo].[Customers] AS [t0] WHERE EXISTS( ??? SELECT NULL AS [EMPTY] ??? FROM ( ??????? SELECT COUNT(*) AS [value], [t1].[CustomerID] ?? ?????FROM [dbo].[Orders] AS [t1] ??????? GROUP BY [t1].[CustomerID] ??????? ) AS [t2] ??? WHERE ([t2].[CustomerID] = [t0].[CustomerID]) AND ([t2].[value] > @p0) ??? ) -- @p0: Input Int32 (Size = 0; Prec = 0; Scale = 0) [5] |
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in操作
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描述：查詢指定城市中的客戶
查詢句法：
| ???? ???var?in操作 = from c in ctx.Customers ??????????????????? where new string[] { "Brandenburg", "Cowes", "Stavern" }.Contains(c.City) ??????????????????? select c; |
對應SQL：
| ?????? SELECT [t0].[CustomerID], [t0].[CompanyName], [t0].[ContactName], [t0].[ContactTitle], [t0].[Address], [t0].[City], [t0].[Region], [t0].[PostalCode], [t0].[Country], [t0].[Phone], [t0].[Fax] FROM [dbo].[Customers] AS [t0] WHERE [t0].[City] IN (@p0, @p1, @p2) -- @p0: Input String (Size = 11; Prec = 0; Scale = 0) [Brandenburg] -- @p1: Input String (Size = 5; Prec = 0; Scale = 0) [Cowes] -- @p2: Input String (Size = 7; Prec = 0; Scale = 0) [Stavern] |
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join
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描述：內連接，沒有分類的產品查詢不到
查詢句法：
| var innerjoin = from p in ctx.Products ??????????????????????? join c in ctx.Categories ??????????????? ????????on p.CategoryID equals c.CategoryID ??????????????????????? select p.ProductName; |
對應SQL：
| SELECT COUNT(*) AS [value] FROM [dbo].[Products] AS [t0] INNER JOIN [dbo].[Categories] AS [t1] ON [t0].[CategoryID] = ([t1].[CategoryID]) |
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描述：外連接，沒有分類的產品也能查詢到
查詢句法：
| var leftjoin = from p in ctx.Products ?????????????????????? join c in ctx.Categories ?????????????????????? on p.CategoryID equals c.CategoryID ?????????????????????? into pro ?????????????????????? from x in pro.DefaultIfEmpty() ???????????????? ??????select p.ProductName; |
對應SQL：
| SELECT COUNT(*) AS [value] FROM [dbo].[Products] AS [t0] LEFT OUTER JOIN [dbo].[Categories] AS [t1] ON [t0].[CategoryID] = ([t1].[CategoryID]) |
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?????? 你可能會很奇怪，原先很復雜的SQL使用查詢句法會很簡單（比如按照條件分組）。但是原先覺得很好理解的SQL使用查詢句法會覺得很復雜（比如連接查詢）。其實，我們還可以通過其它方式進行連接操作，在以后說DataLoadOptions類型的時候會再說。雖然Linq to sql已經非常智能了，但是對于非常復雜的查詢還是建議通過存儲過程實現，下次講解如何調用存儲過程。
轉載于:https://www.cnblogs.com/tgyun/archive/2009/07/30/1535314.html
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