解决.ToPivotTable(it => it.day, it =>new{ it.name}, it => it.Sum(x => x.count))的几个问题

1 it.name 为空值时抛出异常索引超出界值异常
2 当it.name 的值中 有"T0 = T1 = T2"类似情况是会截断字符串，显示为"T0"
3 提升转化效率，现在所花时间只需要之前的1/4左右

Src/Asp.NetCore2/MySqlTest/a9_ToPivot.cs

@@ -0,0 +1,126 @@
+#region using
+using OrmTest;
+using SqlSugar;
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+#endregion
+
+namespace MySqlTest
+{
+    public class _a9_ToPivot
+    {
+
+        public static void Init()
+        {
+
+            var db = DbHelper.GetNewDb();
+            db.CodeFirst.SetStringDefaultLength(200).InitTables(typeof(RowToColumn));
+            Clean();
+            InitData();
+            Test5();
+            Test6();
+        }
+        public static void InitData()
+        {
+            var db = DbHelper.GetNewDb();
+            var ls = new List<RowToColumn>();
+            // 创建 Stopwatch 对象并开始计时
+            Stopwatch stopwatch = new Stopwatch();
+            stopwatch.Start();
+
+            for (int i = 1; i <= 100 * 10000; i++)
+            {
+                ls.Add(new RowToColumn()
+                {
+                    Id = Guid.NewGuid(),
+                    Code = "A" + i % 1000,
+                    Date = new DateTime(2023, i % 11 + 1, 1),
+                    Date2 = new DateTime(2023, i % 11 + 1, i % 28 + 1, i % 24, i % 60, i % 60),
+                    Val = i % 10,
+                    T1 = i % 3 == 0 ? null : "T0",
+                    T2 = i % 3 == 1 ? null : 3
+                }); ;
+                if (i % 100000 == 0)
+                {
+                    db.Fastest<RowToColumn>().PageSize(100000).BulkCopy(ls);
+                    ls.Clear();
+                }
+            }
+
+            Task.Run(() =>
+            {
+            });
+            // 结束计时并获取经过的时间
+            stopwatch.Stop();
+            TimeSpan elapsedTime = stopwatch.Elapsed;
+
+            Console.WriteLine("T0:" + elapsedTime);
+        }
+        public static void Clean()
+        {
+            var db = DbHelper.GetNewDb();
+            db.DbMaintenance.TruncateTable<RowToColumn>();
+        }
+
+        public static void Test5()
+        {
+            var db = DbHelper.GetNewDb();
+            // 创建 Stopwatch 对象并开始计时
+            Stopwatch stopwatch = new Stopwatch();
+            stopwatch.Start();
+            var s = new DateTime(2023, 2, 1);
+            var e = new DateTime(2023, 6, 1).AddMilliseconds(-1);
+            var ls = db.Queryable<RowToColumn>()
+                .Where(x => x.Date >= s && x.Date <= e)
+                .GroupBy(x => new { x.Code, x.Date, x.Val, x.T1, x.T2 })
+                .Select(x => new { x.Code, x.Date, x.T1, x.T2, Val = SqlFunc.AggregateSum(x.Val) })//求和可以自动处理空值
+                .ToPivotTable(it => it.Code, it => new { it.Date, it.T1, it.T2 }, it => it.Any() ? it.Sum(x => x.Val) : 0);
+
+            // 结束计时并获取经过的时间
+            stopwatch.Stop();
+            TimeSpan elapsedTime = stopwatch.Elapsed;
+
+            Console.WriteLine("T5:" + elapsedTime);
+        }
+        public static void Test6()
+        {
+            var db = DbHelper.GetNewDb();
+            // 创建 Stopwatch 对象并开始计时
+            Stopwatch stopwatch = new Stopwatch();
+            stopwatch.Start();
+            var s = new DateTime(2023, 2, 1);
+            var e = new DateTime(2023, 6, 1).AddMilliseconds(-1);
+            var ls = db.Queryable<RowToColumn>()
+               .Where(x => x.Date >= s && x.Date <= e)
+               .GroupBy(x => new { x.Code, x.Date, x.Val, x.T1, x.T2 })
+               .Select(x => new { x.Code, x.Date, x.T1, x.T2, Val = SqlFunc.AggregateSum(x.Val) })//求和可以自动处理空值
+               .ToPivotList(it => it.Code, it => new { it.Date, it.T1, it.T2 }, it => it.Any() ? it.Sum(x => x.Val) : 0);
+
+            // 结束计时并获取经过的时间
+            stopwatch.Stop();
+            TimeSpan elapsedTime = stopwatch.Elapsed;
+
+            Console.WriteLine("T000:" + elapsedTime);
+        }
+    }
+
+    [SugarTable("row_2_column")]
+    public class RowToColumn
+    {
+        [SugarColumn(IsPrimaryKey = true)]
+        public Guid Id { get; set; }
+        public DateTime Date { get; set; }
+        public DateTime Date2 { get; set; }
+        public string Code { get; set; }
+        public decimal? Val { get; set; }
+        [SugarColumn(ColumnName = "t_1", IsNullable = true)]
+        public string T1 { get; set; }
+        [SugarColumn(ColumnName = "t_2", IsNullable = true)]
+        public int? T2 { get; set; }
+    }
+}