Add demo

Src/Asp.NetCore2/SqlSeverTest/4_Subquery.cs

@@ -0,0 +1,68 @@
+using SqlSugar;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace OrmTest
+{ 
+    public class _4_Subquery
+    {
+        public static void Init()
+        {
+
+            var db = DbHelper.GetNewDb();
+
+            db.CodeFirst.InitTables<Student, School>();
+            db.DbMaintenance.TruncateTable<Student, School>();
+
+            db.Insertable(new Student() { Id = 1, SchoolId = 1 }).ExecuteCommand();
+            db.Insertable(new School() { Id = 1, Name = "Harvard School" }).ExecuteCommand();
+            db.Insertable(new Student() { Id = 2, SchoolId = 2 }).ExecuteCommand();
+            db.Insertable(new School() { Id = 2, Name = "haha School" }).ExecuteCommand();
+
+            //subquery select
+            var result = db.Queryable<Student>()
+               .Select(st => new
+               {
+                   SchoolName = SqlFunc.Subqueryable<School>().Where(s => s.Id == st.SchoolId).Select(s => s.Name),
+                   MaxSchoolId = SqlFunc.Subqueryable<School>().Where(s => s.Id == st.SchoolId).Select(s => SqlFunc.AggregateMax(s.Id)),
+                   MaxSchoolId2 = SqlFunc.Subqueryable<School>().Where(s => s.Id == st.SchoolId).Max(s => s.Id),
+               })
+               .ToList();
+
+            //Exists:
+            //SELECT [Id],[SchoolId] FROM [Student0402] [it]  WHERE (EXISTS ( SELECT * FROM [School0402] [s]  WHERE ( [Id] = [it].[SchoolId] ) ))
+            var result2 = db.Queryable<Student>()
+              .Where(it => SqlFunc.Subqueryable<School>().Where(s => s.Id == it.SchoolId).Any())
+              .ToList();
+
+            //In:
+            //SELECT [Id],[SchoolId] FROM [Student0402] [it]  WHERE  [Id]  in (SELECT [Id] FROM [School0402] [s]  GROUP BY [Id])
+            var result3 = db.Queryable<Student>()
+            .Where(it => it.Id == SqlFunc.Subqueryable<School>().GroupBy(s => s.Id).Select(s => s.Id))
+            .ToList();
+
+            //Equal:
+            //SELECT [Id],[SchoolId] FROM [Student0402] [it]  WHERE ( [Id] =(SELECT TOP 1 [s].[Id] FROM [School0402] [s] ))
+            var result4 = db.Queryable<Student>()
+            .Where(it => it.Id == SqlFunc.Subqueryable<School>().Select(s => s.Id))
+            .ToList();
+        }
+
+        [SugarTable("Student0402")]
+        public class Student
+        {
+            public int Id { get; set; }
+            public int SchoolId { get; set; }
+        }
+        [SugarTable("School0402")]
+        public class School
+        {
+            public int Id { get; set; }
+            public string Name { get; set; }
+        }
+
+    }
+}

Src/Asp.NetCore2/SqlSeverTest/Program.cs

@@ -14,6 +14,7 @@ namespace OrmTest
             _2_DbFirst.Init();
             _3_EasyQuery.Init();
             _4_JoinQuery.Init();
+            _4_Subquery.Init();
             _5_PageQuery.Init();
             _6_NavQuery.Init();
             _7_GroupQuery.Init();