是否可以在此示例中使用递归 CTE？

Question

IF OBJECT_ID('tempdb..#MyTable') IS NOT NULL DROP TABLE #MyTable
create table #MyTable (PolNo varchar(50), ControlNo int, PrevControlNo int, Premim money)
insert into #MyTable values ('Policy-00', 5000, NULL, 1000),
                            ('Policy-01', 6000, 5000, 3200),
                            ('Policy-02', 7000, 6000, 4500),
                            ('Policy-03', 8000, 7000, 3800)
select * from #MyTable

原始输出如下所示：

使用递归CTE是否可以得到如下结果？

我试过类似的方法，但它基本上给了我相同的结果：

;with cte as (
select m.PolNo, m.ControlNo, PrevControlNo, 1 as lvl
from #MyTable m
union all 
select c.PolNo, c.ControlNo, c.PrevControlNo, c.lvl+1
from cte c
inner join #MyTable m ON m.ControlNo = c.PrevControlNo
where c.PrevControlNo IS  NULL
) 
select cte.PolNo,  ControlNo, PrevControlNo
from cte

Answer 1

LEFT JOIN单关就够了:

SELECT *
FROM #MyTable m1
LEFT JOIN #MyTable m2
  ON m2.ControlNo = m1.PrevControlNo;

db<>fiddle demo

是否可以在此示例中使用递归 CTE？

Is it possible to utilize Recursive CTE in this example?

sql-server

tsql

common-table-expression

recursive-query

recursive-cte