处理 Left Join

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我是靠谱客的博主清爽西牛，最近开发中收集的这篇文章主要介绍处理 Left Join，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

处理 Left Join

#r @"C:Program FilesReference AssembliesMicrosoftFramework.NETFrameworkv4.5System.Data.Linq.dll";;
#r @"E:ProjectsF#3FSharp.Data.TypeProviders.dll";;
open Microsoft.FSharp.Data.TypeProviders;;
open System.Linq;;
// Count()、DefaultIfEmpty 在其中
//open System.Data.Linq;;
//open System.Data.Linq.SqlClient;
// SqlMethods 作其中

[<Generate>]
type T0 = SqlDataConnection<"Data Source=.SQLEXPRESS;Initial Catalog=FSharpSample;User ID=sa;Password=FSharpSample1234">

let TypeProvider7() =
    let db = T0.GetDataContext()
    let q0 = query {
        for s in db.Student do
        join (for c in db.Course -> s.StudentID = c.CourseID)
        select s
    }
    let q = query {
        for e in q0.DefaultIfEmpty() do
        select e
    }
    q |> Seq.iter (fun n -> printfn "%A" n.Name)
    q |> Seq.length