- 增加 lambda 表达式树解析子查询 ToList + string.Join() 产生 类似 group_concat 的效果（适配了 sqlserver/pgsql/oracle/mysql/sqlite/达梦/金仓) #405；

FreeSql.Tests/FreeSql.Tests.Provider.Odbc/Dameng/DamengExpression/StringTest.cs

@@ -50,6 +50,36 @@ namespace FreeSql.Tests.Odbc.DamengExpression
             list.Add(g.dameng.Select<TestEqualsGuid>().Where(a => a.id.Equals(Guid.Empty)).ToList());
         }
 
+        [Fact]
+        public void StringJoin()
+        {
+            var fsql = g.dameng;
+            fsql.Delete<StringJoin01>().Where("1=1").ExecuteAffrows();
+            fsql.Insert(new[] { new StringJoin01 { name = "<22><><EFBFBD><EFBFBD>" }, new StringJoin01 { name = "<22>Ϻ<EFBFBD>" }, new StringJoin01 { name = "<22><><EFBFBD><EFBFBD>" }, }).ExecuteAffrows();
+
+            var val1 = string.Join(",", fsql.Select<StringJoin01>().ToList(a => a.name));
+            var val2 = fsql.Select<StringJoin01>().ToList(a => string.Join(",", fsql.Select<StringJoin01>().As("b").ToList(b => b.name)));
+            Assert.Equal(val1, val2[0]);
+
+            val1 = string.Join("**", fsql.Select<StringJoin01>().ToList(a => a.name));
+            val2 = fsql.Select<StringJoin01>().ToList(a => string.Join("**", fsql.Select<StringJoin01>().As("b").ToList(b => b.name)));
+            Assert.Equal(val1, val2[0]);
+
+            val1 = string.Join(",", fsql.Select<StringJoin01>().ToList(a => a.id));
+            val2 = fsql.Select<StringJoin01>().ToList(a => string.Join(",", fsql.Select<StringJoin01>().As("b").ToList(b => b.id)));
+            Assert.Equal(val1, val2[0]);
+
+            val1 = string.Join("**", fsql.Select<StringJoin01>().ToList(a => a.id));
+            val2 = fsql.Select<StringJoin01>().ToList(a => string.Join("**", fsql.Select<StringJoin01>().As("b").ToList(b => b.id)));
+            Assert.Equal(val1, val2[0]);
+        }
+        class StringJoin01
+        {
+            [Column(IsIdentity = true)]
+            public int id { get; set; }
+            public string name { get; set; }
+        }
+
         [Fact]
         public void First()
         {