固定表分层查询的Union All的替代方法

如何解决固定表分层查询的Union All的替代方法

下面的查询很耗时间，是否有没有全部并集的替代方法，我们可以在单个查询中实现吗

仅提供了3个表的样本数据，容易被低估了。

parameters:
- name: branchName
  displayName: 'Repository branch name'
  type: string
- name: WebAppName
  displayName: 'Application name'
  type: string
- name: ServiceConnection
  displayName: 'ServiceConnection name'
  type: string
- name: Workspace
  displayName: 'Workspace name'
  type: string
  
  ##[group]Beginning of a DeployTemplate Parameters
  ##[debug]Debug branchName: ${{parameters.branchName}}
  ##[debug]Debug WebAppName: ${{parameters.WebAppName}}
  ##[debug]Debug ServiceConnection: ${{parameters.ServiceConnection}}
  ##[debug]Debug Workspace: ${{parameters.Workspace}}
  ##[debug]Build.SourceBranchName: variables['Build.SourceBranchName']
  ##[endgroup]

---

 --- GETTING FIRST LEVEL ---
select A,B,C,'PRODUCT' from PRODUCT PR   
left outer join SPB B on B.PRODUCT_id=PR.id
left outer join SPC C on C.PRODUCT_id=PR.id AND C.SPB_ID IS NULL
left outer join SPD D on D.PRODUCT_id=PR.id AND D.SPB_ID IS NULL AND D.SPC_ID IS NULL
LEFT OUTER JOIN SPE E ON E.PRODUCT_ID=PR.id AND E.SPC_ID IS NULL AND E.SPD_ID IS NULL

UNION ALL

--- GETTING RECORDS OF ALL CHILDS WHOSE IMMEDIATE PARENT IS SPB ---
select A,'SPB' from SPB B
left outer join SPC C on C.SPB_id=B.id
left outer join SPD D on D.SPB_id = B.id and D.SPC_id is null
--NO SPD JOIN HERE AS THERE IS NO DIRECT AND RELATION SHIP---

UNION ALL

SELECT A,'SPC' FROM SPC C
left outer join SPD D on D.SPC_ID=C.id AND D.SPB_ID IS NULL 
LEFT OUTER JOIN SPE E ON E.SPC_ID=C.id AND E.SPD_ID IS NULL 

UNION ALL

SELECT A,'SPD' FROM SPD D
LEFT OUTER JOIN SPE E ON E.SPD_ID=D.id AND E.SPC_ID IS NULL 

预期结果：

Table1(Product)        Table2(SPB)      Table3(SPC)
Product ProductName    SPB   P_ID       SPC    SP_B_ID  P_ID
P101     Pname1        B201  P101       C301            P101
P102     Pname2        B202  P103       C302    B201    P101
P103     Pname3        B203  P103       C303    B202    P103
                       B204  P101       C304    B203    P103
                                        C305    B202    P103