本文转自：http://msdn.microsoft.com/zh-cn/library/hh225374.aspx

查询表达式可以查询数据源并将数据是一种预期形式。             查询表达式提供 F# 中支持 LINQ。

 
query { expression }
备注

            

查询表达式是计算表达式的类型类似于序列表达式。               就象通过提供代码指定顺序在序列表达式中，可以在查询表达式指定设置数据通过提供代码。  在序列表达式，yield 关键字标识要返回的数据为产生的序列的一部分。  在查询表达式中，select 关键字执行相同的功能。  除了 select 关键字以外，F# 还支持十分类似于 SQL SELECT 语句的大量查询运算符。  这是一个简单的查询表达式的示例，与连接到 Northwind OData 源的代码。

// Use the OData type provider to create types that can be used to access the Northwind database.

// Add References to FSharp.Data.TypeProviders and System.Data.Services.Client

open Microsoft.FSharp.Data.TypeProviders

type Northwind = ODataService<"http://services.odata.org/Northwind/Northwind.svc">

let db = Northwind.GetDataContext()

// A query expression.

let query1 = query { for customer in db.Customers do

                     select customer }

query1

|> Seq.iter (fun customer -> printfn "Company: %s Contact: %s" customer.CompanyName customer.ContactName)

在前面的代码示例中，查询表达式在大括号。  代码的含义在表达式的是，返回每个客户在 customers 表在查询结果的数据库中。  查询表达式返回实现 IQueryable<T> 和 IEnumerable<T>的类型，并且，因此可重复使用 序列模块，当此示例显示。

每个计算表达式类型从生成器选件类生成。  查询计算表达式的生成器选件类是 QueryBuilder。  有关更多信息，请参见计算表达式 (F#)和Linq.QueryBuilder 类 (F#)。

查询运算符

            

查询运算符在要返回的记录可以指定查询的详细信息，例如放置 standard 或指定结果排序顺序。               查询源必须支持查询运算符。  如果尝试使用不支持的查询运算符，NotSupportedException 将引发异常。

可以转换为 SQL 只的表达式在查询表达式中允许的。               例如，那么，当您使用 where 查询运算符时，在表达式不允许函数调用。

表 1 显示可用的查询运算符。               此外，请参见 Table2 后，比较 SQL 查询和等效的 F# 查询表达式本主题。  某些查询运算符不是由某些类型提供程序支持。  具体而言，OData 类型提供程序在查询运算符绑定到 OData 支持由于限制。  有关更多信息，请参见 ODataService 类型提供程序 (f#)。

此表假定一个数据库为以下形式：

示例数据库关系图                       

代码还在下表中假定下列数据库连接代码。               项目应添加对 System.Data、要求和 FSharp.Data.TypeProviders 程序集。  创建此数据库的代码是组成的本主题末尾的。

open System

open Microsoft.FSharp.Data.TypeProviders

open System.Data.Linq.SqlClient

open System.Linq

open Microsoft.FSharp.Linq

type schema = SqlDataConnection<"Data Source=SERVER\INSTANCE;Initial Catalog=MyDatabase;Integrated Security=SSPI;">

let db = schema.GetDataContext()

// Needed for some query operator examples:

let data = [ 1; 5; 7; 11; 18; 21]
表 1。查询运算符

运算符

描述

contains

确定所选元素是否包含一个指定的元素。

let isStudent11 =

    query {

        for student in db.Student do

        select student.Age.Value

        contains 11

    }

count

返回所选元素的数量。

let countOfStudents =

    query {

        for student in db.Student do

        select student

        count

    }

last

到目前为止选择选定的表的最后一个元素。

let number =

    query {

        for number in data do

        last

    }

lastOrDefault

;如果未找到至此，选择选定的表中的最后一个元素或一个默认值元素。

let number =

    query {

        for number in data do

        where (number < 0)

        lastOrDefault

    }

exactlyOne

到目前为止选定的一个，特定元素。  如果多个元素存在，则将引发。

let student =

    query {

        for student in db.Student do

        where (student.StudentID = 1)

        select student

        exactlyOne

    }

exactlyOneOrDefault

;如果未找到至此，选择选定的表的唯一，特定元素或一个默认值该元素。

let student =

    query {

        for student in db.Student do

        where (student.StudentID = 1)

        select student

        exactlyOneOrDefault

    }

headOrDefault

如果该序列不包含元素至此，选择选定的表的第一个元素或一个默认值。

let student =

    query {

        for student in db.Student do

        select student

        headOrDefault

    }

select

到目前为止项目选定的每个元素。

query {

    for student in db.Student do

    select student

    }

where

根据指定谓词的元素。

query {

    for student in db.Student do

    where (student.StudentID > 4)

    select student

    }

minBy

为选定的每个元素到目前为止选择一个值并返回最小的结果值。

let student =

    query {

        for student in db.Student do

        minBy student.StudentID

    }

maxBy

为选定的每个元素到目前为止选择一个值并返回最大结果值。

let student =

    query {

        for student in db.Student do

        maxBy student.StudentID

    }

groupBy

到目前为止组按照指定的键选择器中选择的元素。

query {

    for student in db.Student do

    groupBy student.Age into g

    select (g.Key, g.Count())

    }

sortBy

到目前为止对升序选择组件的特定排序的键。

query {

    for student in db.Student do

    sortBy student.Name

    select student

}

sortByDescending

到目前为止按降序进行选择的元素由特定排序的键。

query {

    for student in db.Student do

    sortByDescending student.Name

    select student

}

thenBy

在升序到目前为止执行特定排序的键选择哪个后续排序元素。  此运算符只能在 sortBy、sortByDescending、thenBy或 thenByDescending之后只使用。

query {

    for student in db.Student do

    where student.Age.HasValue

    sortBy student.Age.Value

    thenBy student.Name

    select student

}

thenByDescending

按降序到目前为止执行特定排序的键选择哪个后续排序元素。  此运算符只能在 sortBy、sortByDescending、thenBy或 thenByDescending之后只使用。

query {

    for student in db.Student do

    where student.Age.HasValue

    sortBy student.Age.Value

    thenByDescending student.Name

    select student

}

groupValBy

为给定键选择和组至此选择一个值元素的每个元素。

query {

    for student in db.Student do

    groupValBy student.Name student.Age into g

    select (g, g.Key, g.Count())

    }

join

相互关系两个基于匹配的键的设置选定的值。  请注意键的顺序在周围的 = 签名连接表达式是有意义的。  在连接，因此，如果行。-> 符号后拆分，缩进的缩进距离必须至少在关键字 for。

query {

    for student in db.Student do

    join selection in db.CourseSelection on

          (student.StudentID = selection.StudentID)

    select (student, selection)

}

groupJoin

相互关系两个基于匹配的键和组的设置选定的值结果。  请注意键的顺序在周围的 = 签名连接表达式是有意义的。

query {

    for student in db.Student do

    groupJoin courseSelection in db.CourseSelection on

               (student.StudentID = courseSelection.StudentID) into g

    for courseSelection in g do

    join course in db.Course on (courseSelection.CourseID = course.CourseID)

    select (student.Name, course.CourseName)

    }

leftOuterJoin

相互关系两个基于匹配的键和组的设置选定的值结果。  如果任何组为空，使用一组具有一个默认值。  请注意键的顺序在周围的 = 签名连接表达式是有意义的。

query {

    for student in db.Student do

    leftOuterJoin selection in db.CourseSelection on

                   (student.StudentID = selection.StudentID) into result

    for selection in result.DefaultIfEmpty() do

    select (student, selection)

    }

sumByNullable

为选定的每个元素到目前为止选择一个可以为 null 的值并返回这些值的总和。  如果有可以为 null，可不具有值，它将被忽略。

query {

    for student in db.Student do

    sumByNullable student.Age

}

minByNullable

为选定的每个元素到目前为止选择一个可以为 null 的值并返回这些值最小位数。  如果有可以为 null，可不具有值，它将被忽略。

query {

    for student in db.Student do

    minByNullable student.Age

}

maxByNullable

为选定的每个元素到目前为止选择一个可以为 null 的值并返回这些值最大次数。  如果有可以为 null，可不具有值，它将被忽略。

query {

    for student in db.Student do

    maxByNullable student.Age

    }

averageByNullable

为选定的每个元素到目前为止选择一个可以为 null 的值并返回平均值这些值。  如果有可以为 null，可不具有值，它将被忽略。

query {

    for student in db.Student do

    averageByNullable (Nullable.float student.Age)

    }

averageBy

为选定的每个元素到目前为止选择一个值并返回平均值这些值。

query {

    for student in db.Student do

    averageBy (float student.StudentID)

}

distinct

到目前为止选择不同的组件从所选元素。

query {

    for student in db.Student do

    join selection in db.CourseSelection on

          (student.StudentID = selection.StudentID)

    distinct       

}

exists

确定选定的任何元素到目前为止是否满足条件。

query {

    for student in db.Student do

    where (query { for courseSelection in db.CourseSelection do

                   exists (courseSelection.StudentID = student.StudentID) })

    select student

}

find

选择到目前为止满足指定条件的第一个选定的元素。

query {

    for student in db.Student do

    find (student.Name = "Abercrombie, Kim")

}

all

确定选定的所有元素到目前为止是否满足条件。

query {

    for student in db.Student do

    all (SqlMethods.Like(student.Name, "%,%"))

}

head

到目前为止选择第一个元素从选定的表。

query {

    for student in db.Student do

    head

}

nth

到目前为止选择元素在选定的表中的指定索引。

query {

    for numbers in data do

    nth 3

}

skip

到目前为止跳过所选元素指定数目的然后选择剩余的元素。

query {

    for student in db.Student do

    skip 1

}

skipWhile

在序列中的元素，只要一个指定的条件为 true 的然后选择剩余的元素。

query {

    for number in data do

    skipWhile (number < 3)

    select student

    }

sumBy

为选定的每个元素到目前为止选择一个值并返回这些值的总和。

query {

   for student in db.Student do

   sumBy student.StudentID

   }

take

到目前为止选择连续的指定数量的元素从选定的表。

query {

   for student in db.Student do

   select student

   take 2

   }

takeWhile

选择元素序列，只要一个指定条件为 true，则跳过剩余的元素。

query {

    for number in data do

    takeWhile (number < 10)

    }

sortByNullable

到目前为止对升序选择的元素由特定的排序的键。

query {

    for student in db.Student do

    sortByNullable student.Age

    select student

}

sortByNullableDescending

到目前为止按降序进行选择的元素由特定的排序的键。

query {

    for student in db.Student do

    sortByNullableDescending student.Age

    select student

}

thenByNullable

在升序到目前为止执行特定的排序的键选择哪个后续排序元素。  此运算符只能在 sortBy之后只使用、sortByDescending、thenBy或 thenByDescending，也可以为 null 的变量。

query {

    for student in db.Student do

    sortBy student.Name

    thenByNullable student.Age

    select student

}

thenByNullableDescending

按降序到目前为止执行特定的排序的键选择哪个后续排序元素。  此运算符只能在 sortBy之后只使用、sortByDescending、thenBy或 thenByDescending，也可以为 null 的变量。

query {

    for student in db.Student do

    sortBy student.Name

    thenByNullableDescending student.Age

    select student

}

下表显示了 F# 的一些常见 Transact-SQL 查询与其等效项。               代码此表还假定数据库和上表与同一初始代码相同的设置类型提供程序。

表 2。Transact-SQL 和 F# 查询表达式

Transact-SQL (不区分大小写)

F# 查询表达式 (区分大小写)

选择所有字段从表。

SELECT * FROM Student

// All students.

query {

    for student in db.Student do

    select student

}

计数记录在表中。

SELECT COUNT(*) FROM Student

// Count of students.

query {

    for student in db.Student do       

    count

}

EXISTS

SELECT * FROM Student

WHERE EXISTS

(SELECT * FROM CourseSelection

WHERE CourseSelection.StudentID = Student.StudentID)

// Find students who have signed up at least one course.

query {

    for student in db.Student do

    where (query { for courseSelection in db.CourseSelection do

                   exists (courseSelection.StudentID = student.StudentID) })

    select student

}

分组

SELECT Student.Age, COUNT(*) FROM Student

GROUP BY Student.Age

// Group by age and count.

query {

    for n in db.Student do

    groupBy n.Age into g

    select (g.Key, g.Count())

}

// OR

query {

    for n in db.Student do

    groupValBy n.Age n.Age into g

    select (g.Key, g.Count())

}

分组加上条件。

SELECT Student.Age, COUNT(*)

FROM Student

GROUP BY Student.Age

HAVING student.Age > 10

// Group students by age where age > 10.

query {

    for student in db.Student do

    groupBy student.Age into g

    where (g.Key.HasValue && g.Key.Value > 10)

    select (g.Key, g.Count())

}

分组的计数情况。

SELECT Student.Age, COUNT(*)

FROM Student

GROUP BY Student.Age

HAVING COUNT(*) > 1

// Group students by age and count number of students

// at each age with more than 1 student.

query {

    for student in db.Student do

    groupBy student.Age into group

    where (group.Count() > 1)

    select (group.Key, group.Count())

}

分组，计数、求和与求平均值计算。

SELECT Student.Age, COUNT(*), SUM(Student.Age) as total

FROM Student

GROUP BY Student.Age

// Group students by age and sum ages.

query {

    for student in db.Student do

    groupBy student.Age into g       

    let total = query { for student in g do

                        sumByNullable student.Age }

    select (g.Key, g.Count(), total)

}

分组，计数和排序由计数。

SELECT Student.Age, COUNT(*) as myCount

FROM Student

GROUP BY Student.Age

HAVING COUNT(*) > 1

ORDER BY COUNT(*) DESC

// Group students by age, count number of students

// at each age, and display all with count > 1

// in descending order of count.

query {

    for student in db.Student do

    groupBy student.Age into g

    where (g.Count() > 1)       

    sortByDescending (g.Count())

    select (g.Key, g.Count())

}

IN     设置指定值

SELECT *

FROM Student

WHERE Student.StudentID IN (1, 2, 5, 10)

// Select students where studentID is one of a given list.

let idQuery = query { for id in [1; 2; 5; 10] do

                      select id }

query {

    for student in db.Student do

    where (idQuery.Contains(student.StudentID))

    select student

}

LIKE   和 TOP。

-- '_e%' matches strings where the second character is 'e'

SELECT TOP 2 * FROM Student

WHERE Student.Name LIKE '_e%'

// Look for students with Name match _e% pattern and take first two.

query {

    for student in db.Student do

    where (SqlMethods.Like( student.Name, "_e%") )

    select student

    take 2  

    }

与设置的模式匹配LIKE。

-- '[abc]%' matches strings where the first character is

-- 'a', 'b', 'c', 'A', 'B', or 'C'

SELECT * FROM Student

WHERE Student.Name LIKE '[abc]%'

open System.Data.Linq.SqlClient;

printfn "\nLook for students with Name matching [abc]%% pattern."

query {

    for student in db.Student do

    where (SqlMethods.Like( student.Name, "[abc]%") )

    select student 

    }

设置了独占模式的LIKE。

-- '[^abc]%' matches strings where the first character is

-- not 'a', 'b', 'c', 'A', 'B', or 'C'

SELECT * FROM Student

WHERE Student.Name LIKE '[^abc]%'

// Look for students with name matching [^abc]%% pattern.

query {

    for student in db.Student do

    where (SqlMethods.Like( student.Name, "[^abc]%") )

    select student 

    }

在一个字段的LIKE，但是，选择一个不同的字段。

SELECT StudentID AS ID FROM Student

WHERE Student.Name LIKE '[^abc]%'

open System.Data.Linq.SqlClient;

printfn "\nLook for students with name matching [^abc]%% pattern and select ID."

query {

    for n in db.Student do

    where (SqlMethods.Like( n.Name, "[^abc]%") )

    select n.StudentID   

    }

|> Seq.iter (fun id -> printfn "%d" id)

LIKE   ，将子字符串搜索。

SELECT * FROM Student

WHERE Student.Name like '%A%'

// Using Contains as a query filter.

query {

    for student in db.Student do

    where (student.Name.Contains("a"))

    select student

}

只有两个表的简单 JOIN。

SELECT * FROM Student

JOIN CourseSelection

ON Student.StudentID = CourseSelection.StudentID

// Join Student and CourseSelection tables.

query {

    for student in db.Student do

    join selection in db.CourseSelection on

          (student.StudentID = selection.StudentID)

    select (student, selection)

}

只有 两个表的LEFT JOIN。

SELECT * FROM

Student LEFT JOIN CourseSelection

ON Student.StudentID = CourseSelection.StudentID

//Left Join Student and CourseSelection tables.

query {

    for student in db.Student do

    leftOuterJoin selection in db.CourseSelection on

                   (student.StudentID = selection.StudentID) into result

    for selection in result.DefaultIfEmpty() do

    select (student, selection)

    }

JOIN   和 COUNT

SELECT COUNT(*) FROM

Student JOIN CourseSelection

ON Student.StudentID = CourseSelection.StudentID

// Join with count.

query {

    for n in db.Student do

    join e in db.CourseSelection on

          (n.StudentID = e.StudentID)

    count       

}

DISTINCT

SELECT DISTINCT StudentID FROM CourseSelection

// Join with distinct.

query {

    for student in db.Student do

    join selection in db.CourseSelection on

          (student.StudentID = selection.StudentID)

    distinct       

}

清单的计数。

SELECT DISTINCT COUNT(StudentID) FROM CourseSelection

// Join with distinct and count.

query {

    for n in db.Student do

    join e in db.CourseSelection on

          n.StudentID = e.StudentID)

    distinct

    count      

}

BETWEEN

SELECT * FROM Student

WHERE Student.Age BETWEEN 10 AND 15

// Selecting students with ages between 10 and 15.

query {

    for student in db.Student do

    where (student.Age ?>= 10 && student.Age ?< 15)

    select student

}

OR

SELECT * FROM Student

WHERE Student.Age =11 OR Student.Age = 12

// Selecting students with age that's either 11 or 12.

query {

    for student in db.Student do

    where (student.Age.Value = 11 || student.Age.Value = 12)

    select student

}

与排序的OR

SELECT * FROM Student

WHERE Student.Age =12 OR Student.Age = 13

ORDER BY Student.Age DESC

// Selecting students in a certain age range and sorting.

query {

    for n in db.Student do

    where (n.Age.Value = 12 || n.Age.Value = 13)

    sortByNullableDescending n.Age

    select n

}

TOP   ，OR和排序。

SELECT TOP 2 student.Name FROM Student

WHERE Student.Age = 11 OR Student.Age = 12

ORDER BY Student.Name DESC

// Selecting students with certain ages,

// taking account of the possibility of nulls.

query {

    for student in db.Student do

    where ((student.Age.HasValue && student.Age.Value = 11) ||

           (student.Age.HasValue && student.Age.Value = 12))

    sortByDescending student.Name

    select student.Name

    take 2

    }

两个查询UNION。

SELECT * FROM Student

UNION

SELECT * FROM lastStudent

// Union of two queries.

module Queries =

    let query1 = query {

            for n in db.Student do

            select (n.Name, n.Age)

        }

    let query2 = query {

            for n in db.LastStudent do

            select (n.Name, n.Age)

            }

    query2.Union (query1)

两个查询的交集。

SELECT * FROM Student

INTERSECT

SELECT * FROM LastStudent

// Intersect of two queries.

module Queries2 =

    let query1 = query {

           for n in db.Student do

           select (n.Name, n.Age)

        }

    let query2 = query {

            for n in db.LastStudent do

            select (n.Name, n.Age)

            }

    query1.Intersect(query2)

CASE   情况。

SELECT student.StudentID,

    CASE Student.Age

        WHEN -1 THEN 100

        ELSE Student.Age

        END,

        Student.Age

from Student

// Using if statement to alter results for special value.

query {

    for student in db.Student do

    select (if student.Age.HasValue && student.Age.Value = -1 then

               (student.StudentID, System.Nullable<int>(100), student.Age)

            else (student.StudentID, student.Age, student.Age))

    }

多个用例。

SELECT Student.StudentID,

    CASE Student.Age

        WHEN -1 THEN 100

        WHEN 0 THEN 1000

        ELSE Student.Age

    END,

    Student.Age

FROM Student

// Using if statement to alter results for special values.

query {

    for student in db.Student do

    select (if student.Age.HasValue && student.Age.Value = -1 then

               (student.StudentID, System.Nullable<int>(100), student.Age)

            elif student.Age.HasValue && student.Age.Value = 0 then

               (student.StudentID, System.Nullable<int>(1000), student.Age)

            else (student.StudentID, student.Age, student.Age))

    }

多个表。

SELECT * FROM Student, Course

// Multiple table select.

query {

        for student in db.Student do

        for course in db.Course do

        select (student, course)

}

多联接。

SELECT Student.Name, Course.CourseName

FROM Student

JOIN CourseSelection

ON CourseSelection.StudentID = Student.StudentID

JOIN Course

ON Course.CourseID = CourseSelection.CourseID

 // Multiple joins.

query {

    for student in db.Student do

    join courseSelection in db.CourseSelection on

        (student.StudentID = courseSelection.StudentID)

    join course in db.Course on

          (courseSelection.CourseID = course.CourseID)

    select (student.Name, course.CourseName)

    }

多个左外部联接。

SELECT Student.Name, Course.CourseName

FROM Student

LEFT OUTER JOIN CourseSelection

ON CourseSelection.StudentID = Student.StudentID

LEFT OUTER JOIN Course

ON Course.CourseID = CourseSelection.CourseID

// Using leftOuterJoin with multiple joins.

query {

    for student in db.Student do

    leftOuterJoin courseSelection in db.CourseSelection on

        (student.StudentID = courseSelection.StudentID) into g1

    for courseSelection in g1.DefaultIfEmpty() do

    leftOuterJoin course in db.Course on

                   (courseSelection.CourseID = course.CourseID) into g2

    for course in g2.DefaultIfEmpty() do

    select (student.Name, course.CourseName)

    }

下面的代码可用于创建这些示例的示例数据库。

SET ANSI_NULLS ON

GO

SET QUOTED_IDENTIFIER ON

GO

USE [master];

GO

IF EXISTS (SELECT * FROM sys.databases WHERE name = 'MyDatabase')

                DROP DATABASE MyDatabase;

GO

-- Create the MyDatabase database.

CREATE DATABASE MyDatabase COLLATE SQL_Latin1_General_CP1_CI_AS;

GO

-- Specify a simple recovery model

-- to keep the log growth to a minimum.

ALTER DATABASE MyDatabase

                SET RECOVERY SIMPLE;

GO

USE MyDatabase;

GO

CREATE TABLE [dbo].[Course] (

    [CourseID]   INT           NOT NULL,

    [CourseName] NVARCHAR (50) NOT NULL,

    PRIMARY KEY CLUSTERED ([CourseID] ASC)

);

CREATE TABLE [dbo].[Student] (

    [StudentID] INT           NOT NULL,

    [Name]      NVARCHAR (50) NOT NULL,

    [Age]       INT           NULL,

    PRIMARY KEY CLUSTERED ([StudentID] ASC)

);

CREATE TABLE [dbo].[CourseSelection] (

    [ID]        INT NOT NULL,

    [StudentID] INT NOT NULL,

    [CourseID]  INT NOT NULL,

    PRIMARY KEY CLUSTERED ([ID] ASC),

    CONSTRAINT [FK_CourseSelection_ToTable] FOREIGN KEY ([StudentID]) REFERENCES [dbo].[Student] ([StudentID]) ON DELETE NO ACTION ON UPDATE NO ACTION,

    CONSTRAINT [FK_CourseSelection_Course_1] FOREIGN KEY ([CourseID]) REFERENCES [dbo].[Course] ([CourseID]) ON DELETE NO ACTION ON UPDATE NO ACTION

);

CREATE TABLE [dbo].[LastStudent] (

    [StudentID] INT           NOT NULL,

    [Name]      NVARCHAR (50) NOT NULL,

    [Age]       INT           NULL,

    PRIMARY KEY CLUSTERED ([StudentID] ASC)

);

-- Insert data into the tables.

USE MyDatabase

INSERT INTO Course (CourseID, CourseName)

VALUES(1, 'Algebra I');

INSERT INTO Course (CourseID, CourseName)

VALUES(2, 'Trigonometry');

INSERT INTO Course (CourseID, CourseName)

VALUES(3, 'Algebra II');

INSERT INTO Course (CourseID, CourseName)

VALUES(4, 'History');

INSERT INTO Course (CourseID, CourseName)

VALUES(5, 'English');

INSERT INTO Course (CourseID, CourseName)

VALUES(6, 'French');

INSERT INTO Course (CourseID, CourseName)

VALUES(7, 'Chinese');

INSERT INTO Student (StudentID, Name, Age)

VALUES(1, 'Abercrombie, Kim', 10);

INSERT INTO Student (StudentID, Name, Age)

VALUES(2, 'Abolrous, Hazen', 14);

INSERT INTO Student (StudentID, Name, Age)

VALUES(3, 'Hance, Jim', 12);

INSERT INTO Student (StudentID, Name, Age)

VALUES(4, 'Adams, Terry', 12);

INSERT INTO Student (StudentID, Name, Age)

VALUES(5, 'Hansen, Claus', 11);

INSERT INTO Student (StudentID, Name, Age)

VALUES(6, 'Penor, Lori', 13);

INSERT INTO Student (StudentID, Name, Age)

VALUES(7, 'Perham, Tom', 12);

INSERT INTO Student (StudentID, Name, Age)

VALUES(8, 'Peng, Yun-Feng', NULL);

INSERT INTO CourseSelection (ID, StudentID, CourseID)

VALUES(1, 1, 2);

INSERT INTO CourseSelection (ID, StudentID, CourseID)

VALUES(2, 1, 3);

INSERT INTO CourseSelection (ID, StudentID, CourseID)

VALUES(3, 1, 5);

INSERT INTO CourseSelection (ID, StudentID, CourseID)

VALUES(4, 2, 2);

INSERT INTO CourseSelection (ID, StudentID, CourseID)

VALUES(5, 2, 5);

INSERT INTO CourseSelection (ID, StudentID, CourseID)

VALUES(6, 2, 6);

INSERT INTO CourseSelection (ID, StudentID, CourseID)

VALUES(7, 2, 3);

INSERT INTO CourseSelection (ID, StudentID, CourseID)

VALUES(8, 3, 2);

INSERT INTO CourseSelection (ID, StudentID, CourseID)

VALUES(9, 3, 1);

INSERT INTO CourseSelection (ID, StudentID, CourseID)

VALUES(10, 4, 2);

INSERT INTO CourseSelection (ID, StudentID, CourseID)

VALUES(11, 4, 5);

INSERT INTO CourseSelection (ID, StudentID, CourseID)

VALUES(12, 4, 2);

INSERT INTO CourseSelection (ID, StudentID, CourseID)

VALUES(13, 5, 3);

INSERT INTO CourseSelection (ID, StudentID, CourseID)

VALUES(14, 5, 2);

INSERT INTO CourseSelection (ID, StudentID, CourseID)

VALUES(15, 7, 3);

下面的代码包含显示在本主题的代码示例。

#if INTERACTIVE

#r "FSharp.Data.TypeProviders.dll"

#r "System.Data.dll"

#r "System.Data.Linq.dll"

#endif

open System

open Microsoft.FSharp.Data.TypeProviders

open System.Data.Linq.SqlClient

open System.Linq

[<Generate>]

type schema = SqlDataConnection<"Data Source=SERVER\INSTANCE;Initial Catalog=MyDatabase;Integrated Security=SSPI;">

let db = schema.GetDataContext()

let student = db.Student

let data = [1; 5; 7; 11; 18; 21]

open System

type Nullable<'T when 'T : ( new : unit -> 'T) and 'T : struct and 'T :> ValueType > with

    member this.Print() =

        if (this.HasValue) then this.Value.ToString()

        else "NULL"

printfn "\ncontains query operator"

query {

    for student in db.Student do

    select student.Age.Value

    contains 11

    }

|> printfn "Is at least one student age 11? %b" 

printfn "\ncount query operator"

query {

    for student in db.Student do

    select student

    count

    }

|> printfn "Number of students: %d" 

printfn "\nlast query operator."

let num =

    query {

        for number in data do

        sortBy number

        last

        }

printfn "Last number: %d" num

open Microsoft.FSharp.Linq

printfn "\nlastOrDefault query operator."

query {

        for number in data do

        sortBy number

        lastOrDefault

        }

|> printfn "lastOrDefault: %d"

printfn "\nexactlyOne query operator."

let student2 =

    query {

        for student in db.Student do

        where (student.StudentID = 1)

        select student

        exactlyOne

        }

printfn "Student with StudentID = 1 is %s" student2.Name

printfn "\nexactlyOneOrDefault query operator."

let student3 =

    query {

        for student in db.Student do

        where (student.StudentID = 1)

        select student

        exactlyOneOrDefault

        }

printfn "Student with StudentID = 1 is %s" student3.Name

printfn "\nheadOrDefault query operator."

let student4 =

    query {

        for student in db.Student do

        select student

        headOrDefault

        }

printfn "head student is %s" student4.Name

printfn "\nselect query operator."

query {

    for student in db.Student do

    select student

    }

|> Seq.iter (fun student -> printfn "StudentID, Name: %d %s" student.StudentID student.Name)

printfn "\nwhere query operator."

query {

    for student in db.Student do

    where (student.StudentID > 4)

    select student

    }

|> Seq.iter (fun student -> printfn "StudentID, Name: %d %s" student.StudentID student.Name)

printfn "\nminBy query operator."

let student5 =

    query {

        for student in db.Student do

        minBy student.StudentID

    }

printfn "\nmaxBy query operator."

let student6 =

    query {

        for student in db.Student do

        maxBy student.StudentID

    }

printfn "\ngroupBy query operator."

query {

    for student in db.Student do

    groupBy student.Age into g

    select (g.Key, g.Count())

    }

|> Seq.iter (fun (age, count) -> printfn "Age: %s Count at that age: %d" (age.Print()) count)

printfn "\nsortBy query operator."

query {

    for student in db.Student do

    sortBy student.Name

    select student

}

|> Seq.iter (fun student -> printfn "StudentID, Name: %d %s" student.StudentID student.Name)

printfn "\nsortByDescending query operator."

query {

    for student in db.Student do

    sortByDescending student.Name

    select student

}

|> Seq.iter (fun student -> printfn "StudentID, Name: %d %s" student.StudentID student.Name)

printfn "\nthenBy query operator."

query {

    for student in db.Student do

    where student.Age.HasValue

    sortBy student.Age.Value

    thenBy student.Name

    select student

}

|> Seq.iter (fun student -> printfn "StudentID, Name: %d %s" student.Age.Value student.Name)

printfn "\nthenByDescending query operator."

query {

    for student in db.Student do

    where student.Age.HasValue

    sortBy student.Age.Value

    thenByDescending student.Name

    select student

}

|> Seq.iter (fun student -> printfn "StudentID, Name: %d %s" student.Age.Value student.Name)

printfn "\ngroupValBy query operator."

query {

    for student in db.Student do

    groupValBy student.Name student.Age into g

    select (g, g.Key, g.Count())

    }

|> Seq.iter (fun (group, age, count) ->

    printfn "Age: %s Count at that age: %d" (age.Print()) count

    group |> Seq.iter (fun name -> printfn "Name: %s" name))

printfn "\n sumByNullable query operator"

query {

    for student in db.Student do

    sumByNullable student.Age

    }

|> (fun sum -> printfn "Sum of ages: %s" (sum.Print()))

printfn "\n minByNullable"

query {

    for student in db.Student do

    minByNullable student.Age

    }

|> (fun age -> printfn "Minimum age: %s" (age.Print()))

printfn "\n maxByNullable"

query {

    for student in db.Student do

    maxByNullable student.Age

    }

|> (fun age -> printfn "Maximum age: %s" (age.Print()))

printfn "\n averageBy"

query {

    for student in db.Student do

    averageBy (float student.StudentID)

    }

|> printfn "Average student ID: %f"

printfn "\n averageByNullable"

query {

    for student in db.Student do

    averageByNullable (Nullable.float student.Age)

    }

|> (fun avg -> printfn "Average age: %s" (avg.Print()))

printfn "\n find query operator"

query {

    for student in db.Student do

    find (student.Name = "Abercrombie, Kim")

}

|> (fun student -> printfn "Found a match with StudentID = %d" student.StudentID)

printfn "\n all query operator"

query {

    for student in db.Student do

    all (SqlMethods.Like(student.Name, "%,%"))

}

|> printfn "Do all students have a comma in the name? %b"

printfn "\n head query operator"

query {

    for student in db.Student do

    head

    }

|> (fun student -> printfn "Found the head student with StudentID = %d" student.StudentID)

printfn "\n nth query operator"

query {

    for numbers in data do

    nth 3

    }

|> printfn "Third number is %d"

printfn "\n skip query operator"

query {

    for student in db.Student do

    skip 1

    }

|> Seq.iter (fun student -> printfn "StudentID = %d" student.StudentID)

printfn "\n skipWhile query operator"

query {

    for number in data do

    skipWhile (number < 3)

    select number

    }

|> Seq.iter (fun number -> printfn "Number = %d" number)

printfn "\n sumBy query operator"

query {

   for student in db.Student do

   sumBy student.StudentID

   }

|> printfn "Sum of student IDs: %d" 

printfn "\n take query operator"

query {

   for student in db.Student do

   select student

   take 2

   }

|> Seq.iter (fun student -> printfn "StudentID = %d" student.StudentID)

printfn "\n takeWhile query operator"

query {

    for number in data do

    takeWhile (number < 10)

    }

|> Seq.iter (fun number -> printfn "Number = %d" number)

printfn "\n sortByNullable query operator"

query {

    for student in db.Student do

    sortByNullable student.Age

    select student

}

|> Seq.iter (fun student ->

    printfn "StudentID, Name, Age: %d %s %s" student.StudentID student.Name (student.Age.Print()))

printfn "\n sortByNullableDescending query operator"

query {

    for student in db.Student do

    sortByNullableDescending student.Age

    select student

}

|> Seq.iter (fun student ->

    printfn "StudentID, Name, Age: %d %s %s" student.StudentID student.Name (student.Age.Print()))

printfn "\n thenByNullable query operator"

query {

    for student in db.Student do

    sortBy student.Name

    thenByNullable student.Age

    select student

}

|> Seq.iter (fun student ->

    printfn "StudentID, Name, Age: %d %s %s" student.StudentID student.Name (student.Age.Print()))

printfn "\n thenByNullableDescending query operator"

query {

    for student in db.Student do

    sortBy student.Name

    thenByNullableDescending student.Age

    select student

}

|> Seq.iter (fun student ->

    printfn "StudentID, Name, Age: %d %s %s" student.StudentID student.Name (student.Age.Print()))

printfn "All students: "

query {

        for student in db.Student do

        select student

    }

    |> Seq.iter (fun student -> printfn "%s %d %s" student.Name student.StudentID (student.Age.Print()))

printfn "\nCount of students: "

query {

        for student in db.Student do       

        count

    }

|>  (fun count -> printfn "Student count: %d" count)

printfn "\nExists."

query {

        for student in db.Student do

        where (query { for courseSelection in db.CourseSelection do

                       exists (courseSelection.StudentID = student.StudentID) })

        select student }

|> Seq.iter (fun student -> printfn "%A" student.Name)

printfn "\n Group by age and count"

query {

        for n in db.Student do

        groupBy n.Age into g

        select (g.Key, g.Count())

}

|> Seq.iter (fun (age, count) -> printfn "%s %d" (age.Print()) count)

printfn "\n Group value by age."

query {

        for n in db.Student do

        groupValBy n.Age n.Age into g

        select (g.Key, g.Count())

    }

|> Seq.iter (fun (age, count) -> printfn "%s %d" (age.Print()) count)

printfn "\nGroup students by age where age > 10."

query {

        for student in db.Student do

        groupBy student.Age into g

       where (g.Key.HasValue && g.Key.Value > 10)

        select (g, g.Key)

}

|> Seq.iter (fun (students, age) ->

    printfn "Age: %s" (age.Value.ToString())

    students

    |> Seq.iter (fun student -> printfn "%s" student.Name))

printfn "\nGroup students by age and print counts of number of students at each age with more than 1 student."

query {

        for student in db.Student do

        groupBy student.Age into group

        where (group.Count() > 1)

        select (group.Key, group.Count())

}

|> Seq.iter (fun (age, ageCount) ->

     printfn "Age: %s Count: %d" (age.Print()) ageCount)

printfn "\nGroup students by age and sum ages."

query {

        for student in db.Student do

        groupBy student.Age into g       

        let total = query { for student in g do sumByNullable student.Age }

        select (g.Key, g.Count(), total)

}

|> Seq.iter (fun (age, count, total) ->

    printfn "Age: %d" (age.GetValueOrDefault())

    printfn "Count: %d" count

    printfn "Total years: %s" (total.ToString()))

printfn "\nGroup students by age and count number of students at each age, and display all with count > 1 in descending order of count."

query {

        for student in db.Student do

        groupBy student.Age into g

        where (g.Count() > 1)       

        sortByDescending (g.Count())

        select (g.Key, g.Count())

}

|> Seq.iter (fun (age, myCount) ->

    printfn "Age: %s" (age.Print())

    printfn "Count: %d" myCount)

printfn "\n Select students from a set of IDs"

let idList = [1; 2; 5; 10]

let idQuery = query { for id in idList do

                      select id }

query {

        for student in db.Student do

        where (idQuery.Contains(student.StudentID))

        select student

        }

|> Seq.iter (fun student ->

    printfn "Name: %s" student.Name)

printfn "\nLook for students with Name match _e%% pattern and take first two."

query {

    for student in db.Student do

    where (SqlMethods.Like( student.Name, "_e%") )

    select student

    take 2  

    }

|> Seq.iter (fun student -> printfn "%s" student.Name)

printfn "\nLook for students with Name matching [abc]%% pattern."

query {

    for student in db.Student do

    where (SqlMethods.Like( student.Name, "[abc]%") )

    select student 

    }

|> Seq.iter (fun student -> printfn "%s" student.Name)

printfn "\nLook for students with name matching [^abc]%% pattern."

query {

    for student in db.Student do

    where (SqlMethods.Like( student.Name, "[^abc]%") )

    select student 

    }

|> Seq.iter (fun student -> printfn "%s" student.Name)

printfn "\nLook for students with name matching [^abc]%% pattern and select ID."

query {

    for n in db.Student do

    where (SqlMethods.Like( n.Name, "[^abc]%") )

    select n.StudentID   

    }

|> Seq.iter (fun id -> printfn "%d" id)

printfn "\n Using Contains as a query filter."

query {

        for student in db.Student do

        where (student.Name.Contains("a"))

        select student

    }

|> Seq.iter (fun student -> printfn "%s" student.Name)

printfn "\nSearching for names from a list."

let names = [|"a";"b";"c"|]

query {

    for student in db.Student do

    if names.Contains (student.Name) then select student }

|> Seq.iter (fun student -> printfn "%s" student.Name)

printfn "\nJoin Student and CourseSelection tables."

query {

        for student in db.Student do

        join (for selection in db.CourseSelection ->

              student.StudentID = selection.StudentID)

        select (student, selection)

    }

|> Seq.iter (fun (student, selection) -> printfn "%d %s %d" student.StudentID student.Name selection.CourseID)

printfn "\nLeft Join Student and CourseSelection tables."

query {

    for student in db.Student do

    leftOuterJoin (for selection in db.CourseSelection ->

                   student.StudentID = selection.StudentID) into result

    for selection in result.DefaultIfEmpty() do

    select (student, selection)

    }

|> Seq.iter (fun (student, selection) ->

    let selectionID, studentID, courseID =

        match selection with

        | null -> "NULL", "NULL", "NULL"

        | sel -> (sel.ID.ToString(), sel.StudentID.ToString(), sel.CourseID.ToString())

    printfn "%d %s %d %s %s %s" student.StudentID student.Name (student.Age.GetValueOrDefault()) selectionID studentID courseID)

printfn "\nJoin with count"

query {

        for n in db.Student do

        join (for e in db.CourseSelection -> n.StudentID = e.StudentID)

        count       

    }

|>  printfn "%d"

printfn "\n Join with distinct."

query {

        for student in db.Student do

        join (for selection in db.CourseSelection ->

              student.StudentID = selection.StudentID)

        distinct       

    }

|> Seq.iter (fun (student, selection) -> printfn "%s %d" student.Name selection.CourseID)

printfn "\n Join with distinct and count."

query {

        for n in db.Student do

        join (for e in db.CourseSelection -> n.StudentID = e.StudentID)

        distinct

        count      

    }

|> printfn "%d"

printfn "\n Selecting students with age between 10 and 15."

query {

        for student in db.Student do

        where (student.Age.Value >= 10 && student.Age.Value < 15)

        select student

    }

|> Seq.iter (fun student -> printfn "%s" student.Name)

printfn "\n Selecting students with age either 11 or 12."

query {

        for student in db.Student do

        where (student.Age.Value = 11 || student.Age.Value = 12)

        select student

    }

|> Seq.iter (fun student -> printfn "%s" student.Name)

printfn "\n Selecting students in a certain age range and sorting."

query {

        for n in db.Student do

        where (n.Age.Value = 12 || n.Age.Value = 13)

        sortByNullableDescending n.Age

        select n

    }

|> Seq.iter (fun student -> printfn "%s %s" student.Name (student.Age.Print()))

printfn "\n Selecting students with certain ages, taking account of possibility of nulls."

query {

        for student in db.Student do

        where ((student.Age.HasValue && student.Age.Value = 11) ||

               (student.Age.HasValue && student.Age.Value = 12))

        sortByDescending student.Name

        select student.Name

        take 2

    }

|> Seq.iter (fun name -> printfn "%s" name)

printfn "\n Union of two queries."

module Queries =

    let query1 = query {

            for n in db.Student do

            select (n.Name, n.Age)

        }

    let query2 = query {

            for n in db.LastStudent do

            select (n.Name, n.Age)

            }

    query2.Union (query1)

    |> Seq.iter (fun (name, age) -> printfn "%s %s" name (age.Print()))

printfn "\n Intersect of two queries."

module Queries2 =

    let query1 = query {

           for n in db.Student do

           select (n.Name, n.Age)

        }

    let query2 = query {

            for n in db.LastStudent do

            select (n.Name, n.Age)

            }

    query1.Intersect(query2)

    |> Seq.iter (fun (name, age) -> printfn "%s %s" name (age.Print()))

printfn "\n Using if statement to alter results for special value."

query {

        for student in db.Student do

        select (if student.Age.HasValue && student.Age.Value = -1 then

                   (student.StudentID, System.Nullable<int>(100), student.Age)

                else (student.StudentID, student.Age, student.Age))

    }

|> Seq.iter (fun (id, value, age) -> printfn "%d %s %s" id (value.Print()) (age.Print()))

printfn "\n Using if statement to alter results special values."

query {

        for student in db.Student do

        select (if student.Age.HasValue && student.Age.Value = -1 then

                   (student.StudentID, System.Nullable<int>(100), student.Age)

                elif student.Age.HasValue && student.Age.Value = 0 then

                    (student.StudentID, System.Nullable<int>(100), student.Age)

                else (student.StudentID, student.Age, student.Age))

    }

|> Seq.iter (fun (id, value, age) -> printfn "%d %s %s" id (value.Print()) (age.Print()))

printfn "\n Multiple table select."

query {

        for student in db.Student do

        for course in db.Course do

        select (student, course)

}

|> Seq.iteri (fun index (student, course) ->

    if (index = 0) then printfn "StudentID Name Age CourseID CourseName"

    printfn "%d %s %s %d %s" student.StudentID student.Name (student.Age.Print()) course.CourseID course.CourseName)

printfn "\nMultiple Joins"

query {

    for student in db.Student do

    join courseSelection in db.CourseSelection on

        (student.StudentID = courseSelection.StudentID)

    join course in db.Course on

          (courseSelection.CourseID = course.CourseID)

    select (student.Name, course.CourseName)

    }

|> Seq.iter (fun (studentName, courseName) -> printfn "%s %s" studentName courseName)

printfn "\nMultiple Left Outer Joins"

query {

   for student in db.Student do

    leftOuterJoin (for courseSelection in db.CourseSelection ->

                   student.StudentID = courseSelection.StudentID) into g1

    for courseSelection in g1.DefaultIfEmpty() do

    leftOuterJoin (for course in db.Course ->

                   courseSelection.CourseID = course.CourseID) into g2

    for course in g2.DefaultIfEmpty() do

    select (student.Name, course.CourseName)

    }

|> Seq.iter (fun (studentName, courseName) -> printfn "%s %s" studentName courseName)

对于完全的输出，当此代码在 F# interactive 时运行。

--> Referenced 'C:\Program Files (x86)\Reference Assemblies\Microsoft\FSharp\3.0\Runtime\v4.0\Type Providers\FSharp.Data.TypeProviders.dll'

--> Referenced 'C:\Windows\Microsoft.NET\Framework\v4.0.30319\System.Data.dll'

--> Referenced 'C:\Windows\Microsoft.NET\Framework\v4.0.30319\System.Data.Linq.dll'

contains query operator

Binding session to 'C:\Users\ghogen\AppData\Local\Temp\tmp5E3C.dll'...  Binding session to 'C:\Users\ghogen\AppData\Local\Temp\tmp611A.dll'...  Is at least one student age 11?  true

count query operator

Number of students: 8

last query operator.  Last number: 21

lastOrDefault query operator.  lastOrDefault: 21

exactlyOne query operator.  Student with StudentID = 1 is Abercrombie, Kim

exactlyOneOrDefault query operator.  Student with StudentID = 1 is Abercrombie, Kim

headOrDefault query operator.  head student is Abercrombie, Kim

select query operator.  StudentID, Name: 1 Abercrombie, Kim

StudentID, Name: 2 Abolrous, Hazen

StudentID, Name: 3 Hance, Jim

StudentID, Name: 4 Adams, Terry

StudentID, Name: 5 Hansen, Claus

StudentID, Name: 6 Penor, Lori

StudentID, Name: 7 Perham, Tom

StudentID, Name: 8 Peng, Yun-Feng

where query operator.  StudentID, Name: 5 Hansen, Claus

StudentID, Name: 6 Penor, Lori

StudentID, Name: 7 Perham, Tom

StudentID, Name: 8 Peng, Yun-Feng

minBy query operator.  maxBy query operator.  groupBy query operator.  Age: NULL Count at that age: 1

Age: 10 Count at that age: 1

Age: 11 Count at that age: 1

Age: 12 Count at that age: 3

Age: 13 Count at that age: 1

Age: 14 Count at that age: 1

sortBy query operator.  StudentID, Name: 1 Abercrombie, Kim

StudentID, Name: 2 Abolrous, Hazen

StudentID, Name: 4 Adams, Terry

StudentID, Name: 3 Hance, Jim

StudentID, Name: 5 Hansen, Claus

StudentID, Name: 8 Peng, Yun-Feng

StudentID, Name: 6 Penor, Lori

StudentID, Name: 7 Perham, Tom

sortByDescending query operator.  StudentID, Name: 7 Perham, Tom

StudentID, Name: 6 Penor, Lori

StudentID, Name: 8 Peng, Yun-Feng

StudentID, Name: 5 Hansen, Claus

StudentID, Name: 3 Hance, Jim

StudentID, Name: 4 Adams, Terry

StudentID, Name: 2 Abolrous, Hazen

StudentID, Name: 1 Abercrombie, Kim

thenBy query operator.  StudentID, Name: 10 Abercrombie, Kim

StudentID, Name: 11 Hansen, Claus

StudentID, Name: 12 Adams, Terry

StudentID, Name: 12 Hance, Jim

StudentID, Name: 12 Perham, Tom

StudentID, Name: 13 Penor, Lori

StudentID, Name: 14 Abolrous, Hazen

thenByDescending query operator.  StudentID, Name: 10 Abercrombie, Kim

StudentID, Name: 11 Hansen, Claus

StudentID, Name: 12 Perham, Tom

StudentID, Name: 12 Hance, Jim

StudentID, Name: 12 Adams, Terry

StudentID, Name: 13 Penor, Lori

StudentID, Name: 14 Abolrous, Hazen

groupValBy query operator.  Age: NULL Count at that age: 1

Name: Peng, Yun-Feng

Age: 10 Count at that age: 1

Name: Abercrombie, Kim

Age: 11 Count at that age: 1

Name: Hansen, Claus

Age: 12 Count at that age: 3

Name: Hance, Jim

Name: Adams, Terry

Name: Perham, Tom

Age: 13 Count at that age: 1

Name: Penor, Lori

Age: 14 Count at that age: 1

Name: Abolrous, Hazen

sumByNullable query operator

Sum of ages: 84

minByNullable

Minimum age: 10

maxByNullable

Maximum age: 14

averageBy

Average student ID: 4.500000

averageByNullable

Average age: 12

find query operator

Found a match with StudentID = 1

all query operator

Do all students have a comma in the name?  true

head query operator

Found the head student with StudentID = 1

nth query operator

Third number is 11

skip query operator

StudentID = 2

StudentID = 3

StudentID = 4

StudentID = 5

StudentID = 6

StudentID = 7

StudentID = 8

skipWhile query operator

Number = 5

Number = 7

Number = 11

Number = 18

Number = 21

sumBy query operator

Sum of student IDs: 36

take query operator

StudentID = 1

StudentID = 2

takeWhile query operator

Number = 1

Number = 5

Number = 7

sortByNullable query operator

StudentID, Name, Age: 8 Peng, Yun-Feng NULL

StudentID, Name, Age: 1 Abercrombie, Kim 10

StudentID, Name, Age: 5 Hansen, Claus 11

StudentID, Name, Age: 7 Perham, Tom 12

StudentID, Name, Age: 3 Hance, Jim 12

StudentID, Name, Age: 4 Adams, Terry 12

StudentID, Name, Age: 6 Penor, Lori 13

StudentID, Name, Age: 2 Abolrous, Hazen 14

sortByNullableDescending query operator

StudentID, Name, Age: 2 Abolrous, Hazen 14

StudentID, Name, Age: 6 Penor, Lori 13

StudentID, Name, Age: 7 Perham, Tom 12

StudentID, Name, Age: 3 Hance, Jim 12

StudentID, Name, Age: 4 Adams, Terry 12

StudentID, Name, Age: 5 Hansen, Claus 11

StudentID, Name, Age: 1 Abercrombie, Kim 10

StudentID, Name, Age: 8 Peng, Yun-Feng NULL

thenByNullable query operator

StudentID, Name, Age: 1 Abercrombie, Kim 10

StudentID, Name, Age: 2 Abolrous, Hazen 14

StudentID, Name, Age: 4 Adams, Terry 12

StudentID, Name, Age: 3 Hance, Jim 12

StudentID, Name, Age: 5 Hansen, Claus 11

StudentID, Name, Age: 8 Peng, Yun-Feng NULL

StudentID, Name, Age: 6 Penor, Lori 13

StudentID, Name, Age: 7 Perham, Tom 12

thenByNullableDescending query operator

StudentID, Name, Age: 1 Abercrombie, Kim 10

StudentID, Name, Age: 2 Abolrous, Hazen 14

StudentID, Name, Age: 4 Adams, Terry 12

StudentID, Name, Age: 3 Hance, Jim 12

StudentID, Name, Age: 5 Hansen, Claus 11

StudentID, Name, Age: 8 Peng, Yun-Feng NULL

StudentID, Name, Age: 6 Penor, Lori 13

StudentID, Name, Age: 7 Perham, Tom 12

All students:

Abercrombie, Kim 1 10

Abolrous, Hazen 2 14

Hance, Jim 3 12

Adams, Terry 4 12

Hansen, Claus 5 11

Penor, Lori 6 13

Perham, Tom 7 12

Peng, Yun-Feng 8 NULL

Count of students:

Student count: 8

Exists.

"  Abercrombie, Kim"

"Abolrous, Hazen"

"Hance, Jim"

"Adams, Terry"

"Hansen, Claus"

"Perham, Tom"

Group by age and count

NULL 1

10 1

11 1

12 3

13 1

14 1

Group value by age.  NULL 1

10 1

11 1

12 3

13 1

14 1

Group students by age where age > 10.  Age: 11

Hansen, Claus

Age: 12

Hance, Jim

Adams, Terry

Perham, Tom

Age: 13

Penor, Lori

Age: 14

Abolrous, Hazen

Group students by age and print counts of number of students at each age with more than 1 student.  Age: 12 Count: 3

Group students by age and sum ages.  Age: 0

Count: 1

Total years:

Age: 10

Count: 1

Total years: 10

Age: 11

Count: 1

Total years: 11

Age: 12

Count: 3

Total years: 36

Age: 13

Count: 1

Total years: 13

Age: 14

Count: 1

Total years: 14

Group students by age and count number of students at each age, and display all with count > 1 in descending order of count.  Age: 12

Count: 3

Select students from a set of IDs

Name: Abercrombie, Kim

Name: Abolrous, Hazen

Name: Hansen, Claus

Look for students with Name match _e% pattern and take first two.  Penor, Lori

Perham, Tom

Look for students with Name matching [abc]% pattern.  Abercrombie, Kim

Abolrous, Hazen

Adams, Terry

Look for students with name matching [^abc]% pattern.  Hance, Jim

Hansen, Claus

Penor, Lori

Perham, Tom

Peng, Yun-Feng

Look for students with name matching [^abc]% pattern and select ID.  3

5

6

7

8

Using Contains as a query filter.  Abercrombie, Kim

Abolrous, Hazen

Hance, Jim

Adams, Terry

Hansen, Claus

Perham, Tom

Searching for names from a list.  Join Student and CourseSelection tables.  2 Abolrous, Hazen 2

3 Hance, Jim 3

5 Hansen, Claus 5

2 Abolrous, Hazen 2

5 Hansen, Claus 5

6 Penor, Lori 6

3 Hance, Jim 3

2 Abolrous, Hazen 2

1 Abercrombie, Kim 1

2 Abolrous, Hazen 2

5 Hansen, Claus 5

2 Abolrous, Hazen 2

3 Hance, Jim 3

2 Abolrous, Hazen 2

3 Hance, Jim 3

Left Join Student and CourseSelection tables.  1 Abercrombie, Kim 10 9 3 1

2 Abolrous, Hazen 14 1 1 2

2 Abolrous, Hazen 14 4 2 2

2 Abolrous, Hazen 14 8 3 2

2 Abolrous, Hazen 14 10 4 2

2 Abolrous, Hazen 14 12 4 2

2 Abolrous, Hazen 14 14 5 2

3 Hance, Jim 12 2 1 3

3 Hance, Jim 12 7 2 3

3 Hance, Jim 12 13 5 3

3 Hance, Jim 12 15 7 3

4 Adams, Terry 12 NULL NULL NULL

5 Hansen, Claus 11 3 1 5

5 Hansen, Claus 11 5 2 5

5 Hansen, Claus 11 11 4 5

6 Penor, Lori 13 6 2 6

7 Perham, Tom 12 NULL NULL NULL

8 Peng, Yun-Feng 0 NULL NULL NULL

Join with count

15

Join with distinct.  Abercrombie, Kim 2

Abercrombie, Kim 3

Abercrombie, Kim 5

Abolrous, Hazen 2

Abolrous, Hazen 5

Abolrous, Hazen 6

Abolrous, Hazen 3

Hance, Jim 2

Hance, Jim 1

Adams, Terry 2

Adams, Terry 5

Adams, Terry 2

Hansen, Claus 3

Hansen, Claus 2

Perham, Tom 3

Join with distinct and count.  15

Selecting students with age between 10 and 15.  Abercrombie, Kim

Abolrous, Hazen

Hance, Jim

Adams, Terry

Hansen, Claus

Penor, Lori

Perham, Tom

Selecting students with age either 11 or 12.  Hance, Jim

Adams, Terry

Hansen, Claus

Perham, Tom

Selecting students in a certain age range and sorting.  Penor, Lori 13

Perham, Tom 12

Hance, Jim 12

Adams, Terry 12

Selecting students with certain ages, taking account of possibility of nulls.  Hance, Jim

Adams, Terry

Union of two queries.  Abercrombie, Kim 10

Abolrous, Hazen 14

Hance, Jim 12

Adams, Terry 12

Hansen, Claus 11

Penor, Lori 13

Perham, Tom 12

Peng, Yun-Feng NULL

Intersect of two queries.  Using if statement to alter results for special value.  1 10 10

2 14 14

3 12 12

4 12 12

5 11 11

6 13 13

7 12 12

8 NULL NULL

Using if statement to alter results special values.  1 10 10

2 14 14

3 12 12

4 12 12

5 11 11

6 13 13

7 12 12

8 NULL NULL

Multiple table select.  StudentID Name Age CourseID CourseName

1 Abercrombie, Kim 10 1 Algebra I

2 Abolrous, Hazen 14 1 Algebra I

3 Hance, Jim 12 1 Algebra I

4 Adams, Terry 12 1 Algebra I

5 Hansen, Claus 11 1 Algebra I

6 Penor, Lori 13 1 Algebra I

7 Perham, Tom 12 1 Algebra I

8 Peng, Yun-Feng NULL 1 Algebra I

1 Abercrombie, Kim 10 2 Trigonometry

2 Abolrous, Hazen 14 2 Trigonometry

3 Hance, Jim 12 2 Trigonometry

4 Adams, Terry 12 2 Trigonometry

5 Hansen, Claus 11 2 Trigonometry

6 Penor, Lori 13 2 Trigonometry

7 Perham, Tom 12 2 Trigonometry

8 Peng, Yun-Feng NULL 2 Trigonometry

1 Abercrombie, Kim 10 3 Algebra II

2 Abolrous, Hazen 14 3 Algebra II

3 Hance, Jim 12 3 Algebra II

4 Adams, Terry 12 3 Algebra II

5 Hansen, Claus 11 3 Algebra II

6 Penor, Lori 13 3 Algebra II

7 Perham, Tom 12 3 Algebra II

8 Peng, Yun-Feng NULL 3 Algebra II

1 Abercrombie, Kim 10 4 History

2 Abolrous, Hazen 14 4 History

3 Hance, Jim 12 4 History

4 Adams, Terry 12 4 History

5 Hansen, Claus 11 4 History

6 Penor, Lori 13 4 History

7 Perham, Tom 12 4 History

8 Peng, Yun-Feng NULL 4 History

1 Abercrombie, Kim 10 5 English

2 Abolrous, Hazen 14 5 English

3 Hance, Jim 12 5 English

4 Adams, Terry 12 5 English

5 Hansen, Claus 11 5 English

6 Penor, Lori 13 5 English

7 Perham, Tom 12 5 English

8 Peng, Yun-Feng NULL 5 English

1 Abercrombie, Kim 10 6 French

2 Abolrous, Hazen 14 6 French

3 Hance, Jim 12 6 French

4 Adams, Terry 12 6 French

5 Hansen, Claus 11 6 French

6 Penor, Lori 13 6 French

7 Perham, Tom 12 6 French

8 Peng, Yun-Feng NULL 6 French

1 Abercrombie, Kim 10 7 Chinese

2 Abolrous, Hazen 14 7 Chinese

3 Hance, Jim 12 7 Chinese

4 Adams, Terry 12 7 Chinese

5 Hansen, Claus 11 7 Chinese

6 Penor, Lori 13 7 Chinese

7 Perham, Tom 12 7 Chinese

8 Peng, Yun-Feng NULL 7 Chinese

Multiple Joins

Abercrombie, Kim Trigonometry

Abercrombie, Kim Algebra II

Abercrombie, Kim English

Abolrous, Hazen Trigonometry

Abolrous, Hazen English

Abolrous, Hazen French

Abolrous, Hazen Algebra II

Hance, Jim Trigonometry

Hance, Jim Algebra I

Adams, Terry Trigonometry

Adams, Terry English

Adams, Terry Trigonometry

Hansen, Claus Algebra II

Hansen, Claus Trigonometry

Perham, Tom Algebra II

Multiple Left Outer Joins

Abercrombie, Kim Trigonometry

Abercrombie, Kim Algebra II

Abercrombie, Kim English

Abolrous, Hazen Trigonometry

Abolrous, Hazen English

Abolrous, Hazen French

Abolrous, Hazen Algebra II

Hance, Jim Trigonometry

Hance, Jim Algebra I

Adams, Terry Trigonometry

Adams, Terry English

Adams, Terry Trigonometry

Hansen, Claus Algebra II

Hansen, Claus Trigonometry

Penor, Lori

Perham, Tom Algebra II

Peng, Yun-Feng 

type schema

val db : schema.ServiceTypes.SimpleDataContextTypes.MyDatabase1

val student : System.Data.Linq.Table<schema.ServiceTypes.Student>

val data : int list = [1; 5; 7; 11; 18; 21]

type Nullable<'T

                when 'T : (new : unit ->  'T) and 'T : struct and

                     'T :> System.ValueType> with

  member Print : unit -> string

val num : int = 21

val student2 : schema.ServiceTypes.Student

val student3 : schema.ServiceTypes.Student

val student4 : schema.ServiceTypes.Student

val student5 : int = 1

val student6 : int = 8

val idList : int list = [1; 2; 5; 10]

val idQuery : seq<int>

val names : string [] = [|"a"; "b"; "c"|]

module Queries = begin

  val query1 : System.Linq.IQueryable<string * System.Nullable<int>>

  val query2 : System.Linq.IQueryable<string * System.Nullable<int>>

end

module Queries2 = begin

  val query1 : System.Linq.IQueryable<string * System.Nullable<int>>

  val query2 : System.Linq.IQueryable<string * System.Nullable<int>>

end
请参见

            

参考

Linq.QueryBuilder 类 (F#)                       

其他资源

F# 语言参考                       
计算表达式 (F#)            

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