项目代码（伪代码）

1、更改前：r1.Concat(r2) //这里会报错

        public IQueryable<General> GetU8SchedulingOrderPlan(DateTime? start, DateTime? end = null)
        {
            var res1 = u8Plan.GetU8SchedulingOrderPlan()
                .Where(e => e.IQtyFjMofy > 0 && (e.IStatus == 1 || e.IStatus == 2) && e.DLastXqdate != null)
                .Select(e => new General
                {
                    Date = e.DLastXqdate,
                    ItemCode = e.CInvCode,
                    CustomerCode = e.CCusCode,
                    Qty = e.IQtyFjMofy ,
                    Type="U8已审批订单"
                });
            return res1;
        }

        public IQueryable<General> GetU8ShippingPlan(DateTime? start, DateTime? end=null)
        {
            var res1 = u8Plan.GetU8ShippingPlan()
                .Select(e => new General
                {
                    Date = e.Dplandldate,
                    ItemCode = e.Cinvcode,
                    CustomerCode = e.Ccuscode,
                    Qty = e.Iquantity,
                    Type = "发货计划"
                });
            return res1;
        }

var r1 = GetU8SchedulingOrderPlan
var r2 = GetU8ShippingPlan()
r1.Concat(r2) 

2、更新后

        public IQueryable<General> GetU8SchedulingOrderPlan(DateTime? start, DateTime? end = null)
        {
            var res1 = u8Plan.GetU8SchedulingOrderPlan()
                .Where(e => e.IQtyFjMofy > 0 && (e.IStatus == 1 || e.IStatus == 2) && e.DLastXqdate != null)
                .Select(e => new General
                {
                    Date = e.DLastXqdate,
                    ItemCode = Convert.ToString(e.CInvCode),
                    CustomerCode = Convert.ToString(e.CCusCode),
                    Qty = (int)e.IQtyFjMofy ,
                    Type="U8已审批订单"
                });
            return res1;
        }

        public IQueryable<General> GetU8ShippingPlan(DateTime? start, DateTime? end=null)
        {
            var res1 = u8Plan.GetU8ShippingPlan()
                .Select(e => new General
                {
                    Date = e.Dplandldate,
                    ItemCode = Convert.ToString(e.Cinvcode),
                    CustomerCode = Convert.ToString(e.Ccuscode),
                    Qty = (int)e.Iquantity,
                    Type = "发货计划"
                });
            return res1;
        }

var r1 = GetU8SchedulingOrderPlan
var r2 = GetU8ShippingPlan()
r1.Concat(r2) //这里会报错

分析：主要原因是string字段和demical字段导致

1、在SQL SERVER中

• stirng类型有长度的区别：nvarchar(50)、nvarchar(60)、nvarchar(max)
• demical类型有精度的区分：decimal(30, 10)、decimal(30, 15)

2、虽然在C#的项目中他们都是decimal、string类型的属性，但是在sql server还有精度的区分
3、Linq中的Concat转成Sql Server的sql是union all语句
4、在SQL SERVER中，可能是union all认为同钟数据类型即使存在精度差异，也可以判定应该合并的两个string类型或demical字段存在不同，而报错无法合并。

解决方案

1、string类型在linq中加上：Convert.ToString()，转成sql就是Convert(nvarchar(max),字段)
2、对于decimal，如果使用Convert.ToDecimal()，也是不行的，这个没办法转成SQL，所以一旦合并还是会报错。目前解决方案是强转成int类型