Expresiones de consulta

  • Artículo

Las expresiones de consulta permiten consultar un origen de datos y colocar los datos en un formulario deseado. Las expresiones de consulta proporcionan compatibilidad con LINQ en F#.

Sintaxis

query { expression }

Comentarios

Las expresiones de consulta son un tipo de expresión de cálculo similar a las expresiones de secuencia. Al igual que para especificar una secuencia se proporciona código en una expresión de secuencia, para especificar un conjunto de datos se proporciona código en una expresión de consulta. En una expresión de secuencia, la palabra clave yield identifica los datos que se van a devolver como parte de la secuencia resultante. En las expresiones de consulta, la palabra clave select realiza la misma función. Además de la palabra clave select, F# también admite una serie de operadores de consulta que son muy similares a las partes de una instrucción SELECT de SQL. Este es un ejemplo de una expresión de consulta simple, junto con código que se conecta al origen OData de Northwind.

// 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
    }

// Print results
query1
|> Seq.iter (fun customer -> printfn "Company: %s Contact: %s" customer.CompanyName customer.ContactName)

En el ejemplo de código anterior, la expresión de consulta está entre llaves. El significado del código de la expresión es devolver todos los clientes de la tabla Customers de la base de datos en los resultados de la consulta. Las expresiones de consulta devuelven un tipo que implementa IQueryable<T> y IEnumerable<T>, por lo que se pueden iterar mediante el módulo Seq como se muestra en el ejemplo.

Cada tipo de expresión de cálculo se crea a partir de una clase de generador. La clase de generador para la expresión de cálculo de consultas es QueryBuilder. Para obtener más información, vea Expresiones de cálculo y Clase QueryBuilder.

Operadores de consulta

Los operadores de consulta permiten especificar los detalles de la consulta, como colocar criterios en los registros que se van a devolver o especificar el criterio de ordenación de los resultados. El origen de la consulta debe admitir el operador de consulta. Si intenta usar un operador de consulta no admitido, se producirá System.NotSupportedException.

Solo se permiten expresiones que se pueden traducir a SQL en expresiones de consulta. Por ejemplo, no se permiten llamadas a funciones en las expresiones cuando se usa el operador de consulta where.

En la tabla 1 se muestran los operadores de consulta disponibles. Además, vea Table2, que compara las consultas SQL y las expresiones de consulta de F# equivalentes más adelante en este tema. Algunos operadores de consulta no son compatibles con algunos proveedores de tipos. En concreto, el proveedor de tipos de OData está limitado en los operadores de consulta que admite debido a limitaciones en OData.

En esta tabla se supone que una base de datos tiene el formato siguiente:

Diagram that shows a sample database.

El código de las tablas siguientes también supone que existe el siguiente código de conexión de base de datos. Los proyectos deben agregar referencias a ensamblados System.Data, System.Data.Linq y FSharp.Data.TypeProviders. El código que crea esta base de datos se incluye al final de este tema.

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]

Tabla 1. Operadores de consulta

Operador Descripción
contains Determina si los elementos seleccionados incluyen un elemento especificado.

query {
    for student in db.Student do
    select student.Age.Value
    contains 11
}
countDevuelve el número de elementos seleccionados.

query {
    for student in db.Student do
    select student
    count
}
lastSelecciona el último elemento de los elementos seleccionados hasta ahora.

query {
    for number in data do
    last
}
lastOrDefaultSelecciona el último elemento de los elementos seleccionados hasta ahora o un valor predeterminado si no se encuentra ningún elemento.

query {
    for number in data do
    where (number < 0)
    lastOrDefault
}
exactlyOneSelecciona el único elemento específico seleccionado hasta ahora. Si hay varios elementos presentes, se produce una excepción.

query {
    for student in db.Student do
    where (student.StudentID = 1)
    select student
    exactlyOne
}
exactlyOneOrDefaultSelecciona el único elemento específico de los elementos seleccionados hasta ahora o un valor predeterminado si no se encuentra ese elemento.

query {
    for student in db.Student do
    where (student.StudentID = 1)
    select student
    exactlyOneOrDefault
}
headOrDefaultDevuelve el primer elemento de los elementos seleccionados hasta ahora o, si la secuencia no contiene elementos, un valor predeterminado.

query {
    for student in db.Student do
    select student
    headOrDefault
}
selectProyecta cada uno de los elementos seleccionados hasta ahora.

query {
    for student in db.Student do
    select student
}
whereSelecciona elementos en función de un predicado especificado.

query {
    for student in db.Student do
    where (student.StudentID > 4)
    select student
}
minBySelecciona un valor para cada elemento seleccionado hasta ahora y devuelve el valor mínimo resultante.

query {
    for student in db.Student do
    minBy student.StudentID
}
maxBySelecciona un valor para cada elemento seleccionado hasta ahora y devuelve el valor máximo resultante.

query {
    for student in db.Student do
    maxBy student.StudentID
}
groupByAgrupa los elementos seleccionados hasta ahora según un selector de claves especificado.

query {
    for student in db.Student do
    groupBy student.Age into g
    select (g.Key, g.Count())
}
sortByOrdena los elementos seleccionados hasta ahora en orden ascendente por la clave de ordenación especificada.

query {
    for student in db.Student do
    sortBy student.Name
    select student
}
sortByDescendingOrdena los elementos seleccionados hasta ahora en orden descendente por la clave de ordenación especificada.

query {
    for student in db.Student do
    sortByDescending student.Name
    select student
}
thenByRealiza una ordenación posterior de los elementos seleccionados hasta ahora en orden ascendente por la clave de ordenación especificada. Este operador solo se puede usar después de sortBy, sortByDescending, thenBy o thenByDescending.

query {
    for student in db.Student do
    where student.Age.HasValue
    sortBy student.Age.Value
    thenBy student.Name
    select student
}
thenByDescendingRealiza una ordenación posterior de los elementos seleccionados hasta ahora en orden descendente por la clave de ordenación especificada. Este operador solo se puede usar después de sortBy, sortByDescending, thenBy o thenByDescending.

query {
    for student in db.Student do
    where student.Age.HasValue
    sortBy student.Age.Value
    thenByDescending student.Name
    select student
}
groupValBySelecciona un valor para cada elemento seleccionado hasta ahora y agrupa los elementos por la clave especificada.

query {
    for student in db.Student do
    groupValBy student.Name student.Age into g
    select (g, g.Key, g.Count())
}
joinCorrelaciona dos conjuntos de valores seleccionados en función de las claves coincidentes. Tenga en cuenta que el orden de las claves alrededor del signo = en una expresión de combinación es significativo. En todas las combinaciones, si la línea se divide después del símbolo ->, la sangría debe aplicarse al menos hasta la palabra clave for.

query {
    for student in db.Student do
    join selection in db.CourseSelection
        on (student.StudentID = selection.StudentID)
    select (student, selection)
}
groupJoinCorrelaciona dos conjuntos de valores seleccionados en función de las claves coincidentes y agrupa los resultados. Tenga en cuenta que el orden de las claves alrededor del signo = en una expresión de combinación es significativo.

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)
}
leftOuterJoinCorrelaciona dos conjuntos de valores seleccionados en función de las claves coincidentes y agrupa los resultados. Si algún grupo está vacío, se usa en su lugar un grupo con un único valor predeterminado. Tenga en cuenta que el orden de las claves alrededor del signo = en una expresión de combinación es significativo.

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)
}
sumByNullableSelecciona un valor que admite valores NULL para cada elemento seleccionado hasta ahora y devuelve la suma de estos valores. Si algún valor que admite un valor NULL no tiene un valor, se omite.

query {
    for student in db.Student do
    sumByNullable student.Age
}
minByNullableSelecciona un valor que admite valores NULL para cada elemento seleccionado hasta ahora y devuelve el mínimo de estos valores. Si algún valor que admite un valor NULL no tiene un valor, se omite.

query {
    for student in db.Student do
    minByNullable student.Age
}
maxByNullableSelecciona un valor que admite valores NULL para cada elemento seleccionado hasta ahora y devuelve el máximo de estos valores. Si algún valor que admite un valor NULL no tiene un valor, se omite.

query {
    for student in db.Student do
    maxByNullable student.Age
}
averageByNullableSelecciona un valor que admite valores NULL para cada elemento seleccionado hasta ahora y devuelve el promedio de estos valores. Si algún valor que admite un valor NULL no tiene un valor, se omite.

query {
    for student in db.Student do
    averageByNullable (Nullable.float student.Age)
}
averageBySelecciona un valor para cada elemento seleccionado hasta ahora y devuelve el promedio de estos valores.

query {
    for student in db.Student do
    averageBy (float student.StudentID)
}
distinctSelecciona elementos distintos de los elementos seleccionados hasta ahora.

query {
    for student in db.Student do
    join selection in db.CourseSelection
        on (student.StudentID = selection.StudentID)
    distinct
}
existsDetermina si algún elemento seleccionado hasta ahora cumple una condición.

query {
    for student in db.Student do
    where
        (query {
            for courseSelection in db.CourseSelection do
            exists (courseSelection.StudentID = student.StudentID) })
    select student
}
findSelecciona el primer elemento seleccionado hasta ahora que satisface una condición especificada.

query {
    for student in db.Student do
    find (student.Name = "Abercrombie, Kim")
}
allDetermina si todos los elementos seleccionados hasta ahora cumplen una condición.

query {
    for student in db.Student do
    all (SqlMethods.Like(student.Name, "%,%"))
}
headSelecciona el primer elemento de los elementos seleccionados hasta ahora.

query {
    for student in db.Student do
    head
}
nthSelecciona el elemento en un índice especificado entre los elementos seleccionados hasta ahora.

query {
    for numbers in data do
    nth 3
}
skipOmite un número especificado de los elementos seleccionados hasta ahora y, a continuación, selecciona los elementos restantes.

query {
    for student in db.Student do
    skip 1
}
skipWhileOmite los elementos de una secuencia en tanto que el valor de una condición especificada sea true y, a continuación, selecciona los elementos restantes.

query {
    for number in data do
    skipWhile (number < 3)
    select student
}
sumBySelecciona un valor para cada elemento seleccionado hasta ahora y devuelve la suma de estos valores.

query {
    for student in db.Student do
    sumBy student.StudentID
}
takeSelecciona un número especificado de elementos contiguos de los elementos seleccionados hasta ahora.

query {
    for student in db.Student do
    select student
    take 2
}
takeWhileSelecciona los elementos de una secuencia siempre que el valor de una condición especificada sea true y luego omite los elementos restantes.

query {
    for number in data do
    takeWhile (number < 10)
}
sortByNullableOrdena los elementos seleccionados hasta ahora en orden ascendente por la clave de ordenación especificada que admite un valor NULL.

query {
    for student in db.Student do
    sortByNullable student.Age
    select student
}
sortByNullableDescendingOrdena los elementos seleccionados hasta ahora en orden descendente por la clave de ordenación especificada que admite un valor NULL.

query {
    for student in db.Student do
    sortByNullableDescending student.Age
    select student
}
thenByNullableRealiza una ordenación posterior de los elementos seleccionados hasta ahora en orden ascendente por la clave de ordenación especificada que admite un valor NULL. Este operador solo se puede usar inmediatamente después de sortBy, sortByDescending, thenBy o thenByDescending, o sus variantes que admiten un valor NULL.

query {
    for student in db.Student do
    sortBy student.Name
    thenByNullable student.Age
    select student
}
thenByNullableDescendingRealiza una ordenación posterior de los elementos seleccionados hasta ahora en orden descendente por la clave de ordenación especificada que admite un valor NULL. Este operador solo se puede usar inmediatamente después de sortBy, sortByDescending, thenBy o thenByDescending, o sus variantes que admiten un valor NULL.

query {
    for student in db.Student do
    sortBy student.Name
    thenByNullableDescending student.Age
    select student
}

Comparación de Transact-SQL y las expresiones de consulta de F#

En la tabla siguiente se muestran algunas consultas Transact-SQL comunes y sus equivalentes en F#. El código de esta tabla también supone la misma base de datos que la tabla anterior y el mismo código inicial para configurar el proveedor de tipos.

Tabla 2. Transact-SQL y expresiones de consulta de F#

Transact-SQL (no distingue mayúsculas de minúsculas) Expresión de consulta en F# (distingue mayúsculas de minúsculas)
Selección de todos los campos de la tabla.
SELECT * FROM Student

// All students.
query {
    for student in db.Student do
    select student
}
Recuento de registros en una tabla.
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
}
Agrupar
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())
}
Agrupación con condición.
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())
}
Agrupación con condición de recuento.
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())
}
Agrupación, recuento y suma.
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)
}
Agrupación, recuento y ordenación por recuento.
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 un conjunto de valores especificados
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 y 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
}
LIKE con conjunto de coincidencias de patrones.
-- '[abc]%' matches strings where the first character is
-- 'a', 'b', 'c', 'A', 'B', or 'C'
SELECT * FROM Student
WHERE Student.Name LIKE '[abc]%'

query {
    for student in db.Student do
    where (SqlMethods.Like( student.Name, "[abc]%") )
    select student
}
LIKE con el patrón de exclusión establecido.
-- '[^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
}
LIKE en un campo, pero seleccione otro campo.
SELECT StudentID AS ID FROM Student
WHERE Student.Name LIKE '[^abc]%'

query {
    for n in db.Student do
    where (SqlMethods.Like( n.Name, "[^abc]%") )
    select n.StudentID
}
LIKE, con búsqueda en substring.
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
}
JOIN simple con dos tablas.
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)
}
LEFT JOIN con dos tablas.
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 con 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
}
Recuento de valores únicos.
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 &#124;&#124; student.Age.Value = 12)
    select student
}
OR con ordenación
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 &#124;&#124; n.Age.Value = 13)
    sortByNullableDescending n.Age
    select n
}
TOP, OR y ordenación.
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) &#124;&#124;
         (student.Age.HasValue && student.Age.Value = 12))
    sortByDescending student.Name
    select student.Name
    take 2
}
UNION de dos consultas.
SELECT * FROM Student
UNION
SELECT * FROM lastStudent

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)
Intersección de dos consultas.
SELECT * FROM Student
INTERSECT
SELECT * FROM LastStudent

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)
condición CASE.
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))
}
Varios casos.
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))
}
Varias tablas.
SELECT * FROM Student, Course

// Multiple table select.
query {
    for student in db.Student do
    for course in db.Course do
    select (student, course)
}
Varias combinaciones.
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)
}
Varias combinaciones externas izquierdas.
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)
}

El código siguiente se puede usar para crear la base de datos de muestra para estos ejemplos.

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);

El código siguiente contiene el código de ejemplo que aparece en este tema.

#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

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

let db = schema.GetDataContext()

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

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 selection in db.CourseSelection
        on (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 selection in db.CourseSelection
        on (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 e in db.CourseSelection
        on (n.StudentID = e.StudentID)
    count
}
|> printfn "%d"

printfn "\n Join with distinct."
query {
    for student in db.Student do
    join selection in db.CourseSelection
        on (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 e in db.CourseSelection
        on (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 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)
}
|> Seq.iter (fun (studentName, courseName) -> printfn "%s %s" studentName courseName)

Y esta es la salida completa cuando este código se ejecuta en F# interactivo.

--> 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

Vea también