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sql-servert-sqlcommon-table-expressionrecursive-queryrecursive-cte

Is it possible to utilize Recursive CTE in this example?


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

Raw output looks like this:

![PolNo ControlNo   PrevControlNo   Premim
Policy-00   5000    NULL    1000.00
Policy-01   6000    5000    3200.00
Policy-02   7000    6000    4500.00
Policy-03   8000    7000    3800.00


Using the recursive CTE is it possible to get the result like below?

enter image description here

I tried something like this, but it basically gives me the same result:

;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

Solution

  • LEFT JOIN is enough for single level:

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

    db<>fiddle demo