SQL IDENTITY(int,1,1) 用法

select IDENTITY(int,1,1) as SortID from  tb_order

仅当 SELECT 语句中有 INTO 子句时，才能使用 IDENTITY 函数。

select IDENTITY(int,1,1) as SortID,* into #Temp from tb_order

无法使用 SELECT INTO 语句将标识列添加到表 '#Temp'，该表的列 'ID' 已继承了标识属性。

这样写才是正确的，select 后面不能包含*，不能包含ID号，必须写字段名
select IDENTITY(int,1,1) as SortID,OrderNumber into #Temp from tb_order

select *from #Temp

多表获取ID号

select IDENTITY(int,1,1) as SortID,OrderNumber,a.ID as ID into #Temp from tb_order as a
left join tb_OrderList as b on a.ID=b.OrderID

单表获取ID号，直接写ID会报错的

select IDENTITY(int,1,1) as SortID,OrderNumber,a.ID*1 as ID into #Temp from tb_order as a

 ROW_NUMBER()   这样写可以代替
select  ROW_NUMBER()over(order by id) as SortID   from  tb_order
同样获取SortID     IDENTITY(int,1,1) 查询速度会快很多