FreeSql （十九）多表查詢

多表查詢，常用的有聯(lián)表 LeftJoin/InnerJoin/RightJoin ，這三個(gè)方法在上篇文章
<https://www.cnblogs.com/FreeSql/p/11531346.html>已經(jīng)介紹過(guò)。

除了聯(lián)表，還有子查詢 Where Exists，和 Select 子表：
IFreeSql fsql = new FreeSql.FreeSqlBuilder()
.UseConnectionString(FreeSql.DataType.MySql, "Data
Source=127.0.0.1;Port=3306;User ID=root;Password=root;Initial
Catalog=cccddd;Charset=utf8;SslMode=none;Max pool size=10") .Build();
[Table(Name = "tb_topic")] class Topic { [Column(IsIdentity = true, IsPrimary =
true)] public int Id { get; set; } public int Clicks { get; set; } public int
TestTypeInfoGuid { get; set; } public string Title { get; set; } public
DateTime CreateTime { get; set; } }
子表 Exists
var sql2222 = fsql.Select<Topic>().Where(a => fsql.Select<Topic>().Where(b =>
b.Id == a.Id).Any()).ToList(); // SELECT a.`Id`, a.`TypeGuid`, a.`Title`,
a.`CreateTime` // FROM `xxx` a // WHERE (exists(SELECT 1 // FROM `xxx` b //
WHERE (b.`Id` = a.`Id`))) //兩級(jí)相同的子表查詢 sql2222 = fsql.Select<Topic>().Where(a =>
fsql.Select<Topic>().Where(b => b.Id == a.Id && fsql.Select<Topic>().Where(c =>
c.Id == b.Id).Where(d => d.Id == a.Id).Where(e => e.Id == b.Id) .Offset(a.Id)
.Any() ).Any() ).ToList(); // SELECT a.`Id`, a.`TypeGuid`, a.`Title`,
a.`CreateTime` // FROM `xxx` a // WHERE (exists(SELECT 1 // FROM `xxx` b //
WHERE (b.`Id` = a.`Id` AND exists(SELECT 1 // FROM `xxx` c // WHERE (c.`Id` =
b.`Id`) AND (c.`Id` = a.`Id`) AND (c.`Id` = b.`Id`) // limit 0,1)) // limit
0,1))
子表 First/Count/Sum/Max/Min/Avg
var subquery = fsql.Select<Topic>().ToSql(a => new { all = a, first =
fsql.Select<Child>().Where(b => b.ParentId == a.Id).First(b => b.Id), count =
fsql.Select<Child>().Where(b => b.ParentId == a.Id).Count(), sum =
fsql.Select<Child>().Where(b => b.ParentId == a.Id).Sum(b => b.Score), max =
fsql.Select<Child>().Where(b => b.ParentId == a.Id).Max(b => b.Score), min =
fsql.Select<Child>().Where(b => b.ParentId == a.Id).Min(b => b.Score), avg =
fsql.Select<Child>().Where(b => b.ParentId == a.Id).Avg(b => b.Score) });
系列文章導(dǎo)航

*
（一）入門 <https://www.cnblogs.com/FreeSql/p/11531300.html>

*
（二）自動(dòng)遷移實(shí)體 <https://www.cnblogs.com/FreeSql/p/11531301.html>

*
（三）實(shí)體特性 <https://www.cnblogs.com/FreeSql/p/11531302.html>

*
（四）實(shí)體特性 Fluent Api <https://www.cnblogs.com/FreeSql/p/11531304.html>

*
（五）插入數(shù)據(jù) <https://www.cnblogs.com/FreeSql/p/11531306.html>

*
（六）批量插入數(shù)據(jù) <https://www.cnblogs.com/FreeSql/p/11531309.html>

*
（七）插入數(shù)據(jù)時(shí)忽略列 <https://www.cnblogs.com/FreeSql/p/11531316.html>

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（八）插入數(shù)據(jù)時(shí)指定列 <https://www.cnblogs.com/FreeSql/p/11531318.html>

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（九）刪除數(shù)據(jù) <https://www.cnblogs.com/FreeSql/p/11531320.html>

*
（十）更新數(shù)據(jù) <https://www.cnblogs.com/FreeSql/p/11531321.html>

*
（十一）更新數(shù)據(jù) Where <https://www.cnblogs.com/FreeSql/p/11531324.html>

*
（十二）更新數(shù)據(jù)時(shí)指定列 <https://www.cnblogs.com/FreeSql/p/11531327.html>

*
（十三）更新數(shù)據(jù)時(shí)忽略列 <https://www.cnblogs.com/FreeSql/p/11531334.html>

*
（十四）批量更新數(shù)據(jù) <https://www.cnblogs.com/FreeSql/p/11531335.html>

*
（十五）查詢數(shù)據(jù) <https://www.cnblogs.com/FreeSql/p/11531339.html>

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（十六）分頁(yè)查詢 <https://www.cnblogs.com/FreeSql/p/11531341.html>

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（十七）聯(lián)表查詢 <https://www.cnblogs.com/FreeSql/p/11531346.html>

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（十八）導(dǎo)航屬性 <https://www.cnblogs.com/FreeSql/p/11531352.html>

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（十九）多表查詢

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（二十）多表查詢 WhereCascade <https://www.cnblogs.com/FreeSql/p/11531372.html>

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（二十一）查詢返回?cái)?shù)據(jù) <https://www.cnblogs.com/FreeSql/p/11531376.html>

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（二十二）Dto 映射查詢 <https://www.cnblogs.com/FreeSql/p/11531381.html>

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（二十三）分組、聚合 <https://www.cnblogs.com/FreeSql/p/11531384.html>

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（二十四）Linq To Sql 語(yǔ)法使用介紹 <https://www.cnblogs.com/FreeSql/p/11531392.html>

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（二十五）延時(shí)加載 <https://www.cnblogs.com/FreeSql/p/11531395.html>

*
（二十六）貪婪加載 Include、IncludeMany、Dto、ToList
<https://www.cnblogs.com/FreeSql/p/11531404.html>

*
（二十七）將已寫(xiě)好的 SQL 語(yǔ)句，與實(shí)體類映射進(jìn)行二次查詢
<https://www.cnblogs.com/FreeSql/p/11531416.html>

*
（二十八）事務(wù) <https://www.cnblogs.com/FreeSql/p/11531423.html>

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（二十九）Lambda 表達(dá)式 <https://www.cnblogs.com/FreeSql/p/11531425.html>

*
（三十）讀寫(xiě)分離 <https://www.cnblogs.com/FreeSql/p/11531430.html>

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（三十一）分區(qū)分表 <https://www.cnblogs.com/FreeSql/p/11531435.html>

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（三十二）Aop <https://www.cnblogs.com/FreeSql/p/11531471.html>

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（三十三）CodeFirst 類型映射 <https://www.cnblogs.com/FreeSql/p/11531543.html>

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（三十四）CodeFirst 遷移說(shuō)明 <https://www.cnblogs.com/FreeSql/p/11531550.html>

*
（三十五）CodeFirst 自定義特性 <https://www.cnblogs.com/FreeSql/p/11531576.html>

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