停止递归一旦条件满足

Question

我正在使用CTE来爆炸物料清单并需要找到所有那些具有递归组件的物料。

我试图，是限制的周期（级别）的数量深，由子节点设置BOM_Level开往最大：

exec  pr_sys_drop_object '#BOMExploded' 
;with BOM 
as 
(
    select 
     Prod_Plant_CD 
    , Demand_Plant_CD 
    , material_cd 
    , component_cd 
    , component_quantity 
    , component_quantity AS Calculated_Component_Quantity 
    , BOM_Level 
    , Demand_Quantity 
    , CONVERT(float,1)  AS Produced_Ratio 
    , Material_CD   AS Demand_Material_CD 
    from #firstLevel a 
    UNION ALL 
    SELECT 
     b.Plant_CD as 'Prod_Plant_CD' 
    , a.Demand_Plant_CD 
    , b.Material_CD 
    , b.Component_CD 
    , b.component_quantity 
    , b.component_quantity 
    , a.BOM_Level + 1 
    , a.Demand_Quantity 
    , a.Produced_Ratio * a.Component_Quantity  -- Produced Quantity for the current level = Produced Quantity (level -1) * Component_Quantity (level -1) 
    , a.Demand_Material_CD 
    FROM BOM a 
    inner join #BOM_ProdVersion_Priority b 
     on a.component_cd = b.material_cd 
    inner join #base_routes c 
     on a.Demand_Plant_CD = c.Recipient_Plant_CD 
     and b.Plant_CD  = c.Source_Plant_CD 
     and c.Material_CD  = b.Material_CD -- Need to have material_cd to link 
    where b.Material_CD != b.Component_CD 
    and b.Component_Quantity > 0 
    and BOM_Level < 5 -- Give the max number of levels deep we are allowed to cyncle to 
) 

select * 
into #BOMExploded 
from BOM 
OPTION (MAXRECURSION 20) 

然而，使用这种方法，将需要后进程定位何时启动递归组件级别的循环，然后返回跟踪。

如何在给定条件下停止CTE递归查询？

ie. when top-level material_cd = component_cd for a deeper BOM_Level

Answer 1

如果我理解正确的话，你并不需要停止在某一深度/水平，或者说你想停止在一定的水平，但你也需要停止的情况下，你开始反复循环材料。

在下面的递归路径的情况下：mat_1 - >mat_2 - >mat_3 - >mat_1，你想阻止，去年mat_1再次开始骑自行车mat_2等之前。

如果这是正确的，那么你最好的选择是一个Path字段添加到您的递归查询跟踪每一个找到任期下移的递归路径：

exec  pr_sys_drop_object '#BOMExploded' 
;with BOM 
as 
(
    select 
     Prod_Plant_CD 
    , Demand_Plant_CD 
    , material_cd 
    , component_cd 
    , component_quantity 
    , component_quantity AS Calculated_Component_Quantity 
    , BOM_Level 
    , Demand_Quantity 
    , CONVERT(float,1)  AS Produced_Ratio 
    , Material_CD   AS Demand_Material_CD 
    , CAST(material_cd AS VARCHAR(100)) AS Path 
    from #firstLevel a 
    UNION ALL 
    SELECT 
     b.Plant_CD as 'Prod_Plant_CD' 
    , a.Demand_Plant_CD 
    , b.Material_CD 
    , b.Component_CD 
    , b.component_quantity 
    , b.component_quantity 
    , a.BOM_Level + 1 
    , a.Demand_Quantity 
    , a.Produced_Ratio * a.Component_Quantity  -- Produced Quantity for the current level = Produced Quantity (level -1) * Component_Quantity (level -1) 
    , a.Demand_Material_CD 
    , a.Path + '|' + b.material_cd 
    FROM BOM a 
    inner join #BOM_ProdVersion_Priority b 
     on a.component_cd = b.material_cd 
    inner join #base_routes c 
     on a.Demand_Plant_CD = c.Recipient_Plant_CD 
     and b.Plant_CD  = c.Source_Plant_CD 
     and c.Material_CD  = b.Material_CD -- Need to have material_cd to link 
    where b.Material_CD != b.Component_CD 
    and b.Component_Quantity > 0 
    and BOM_Level < 5 -- Give the max number of levels deep we are allowed to cyncle to 
    and a.path NOT LIKE '%' + b.material_cd + '%' 
) 

select * 
into #BOMExploded 
from BOM 
OPTION (MAXRECURSION 20) 

现在你有一个path那是由管道分隔的，您可以测试当前的material_cd以查看它是否已在path中。如果是这样，那么你结束递归的那一段，以防止骑车。

---

更新包括一个版本，我们捕捉material_cd周期，只报告那些在递归的终点：

exec  pr_sys_drop_object '#BOMExploded' 
;with BOM 
as 
(
    select 
     Prod_Plant_CD 
    , Demand_Plant_CD 
    , material_cd 
    , component_cd 
    , component_quantity 
    , component_quantity AS Calculated_Component_Quantity 
    , BOM_Level 
    , Demand_Quantity 
    , CONVERT(float,1)  AS Produced_Ratio 
    , Material_CD   AS Demand_Material_CD 
    , CAST(material_cd AS VARCHAR(100)) AS Path 
    , CAST(NULL AS CHAR(5)) as Cycle_Flag 
    , 0 as Cycle_Depth 
    from #firstLevel a 
    UNION ALL 
    SELECT 
     b.Plant_CD as 'Prod_Plant_CD' 
    , a.Demand_Plant_CD 
    , b.Material_CD 
    , b.Component_CD 
    , b.component_quantity 
    , b.component_quantity 
    , a.BOM_Level + 1 
    , a.Demand_Quantity 
    , a.Produced_Ratio * a.Component_Quantity  -- Produced Quantity for the current level = Produced Quantity (level -1) * Component_Quantity (level -1) 
    , a.Demand_Material_CD 
    , a.Path + '|' + b.material_cd 
    , CASE WHEN a.path NOT LIKE '%' + b.material_cd + '%' then 'Cycle' END AS Cycle_Flag, 
    , CASE WHEN a.path NOT LIKE '%' + b.material_cd + '%' then a.Cycle_Depth + 1 END as Cycle_Depth 
    FROM BOM a 
    inner join #BOM_ProdVersion_Priority b 
     on a.component_cd = b.material_cd 
    inner join #base_routes c 
     on a.Demand_Plant_CD = c.Recipient_Plant_CD 
     and b.Plant_CD  = c.Source_Plant_CD 
     and c.Material_CD  = b.Material_CD -- Need to have material_cd to link 
    where b.Material_CD != b.Component_CD 
    and b.Component_Quantity > 0  
    and a.cycle_depth < 2 --stop the query if we start cycling, but only after we capture at least one full cycle 
) 

select * 
into #BOMExploded 
from BOM 
WHERE cycle_flag IS NOT NULL 
OPTION (MAXRECURSION 20) 

这将捕获cycle_depth这是衡量如何深入到一个循环的计数器我们得到了。我们在达到1的cycle_depth后停止递归，以便在最终选择中捕获循环。