如何在 BigQuery 中显示多层次树结构

Question

我正在处理主管及其下属员工的树状层次结构。难的是有的主管是其他主管下属的员工，而且还很多

对于SQL我从class获得的查询，只有简单的自连接，可能只有两个级别：A被B监督，仅此而已。

但现实世界的问题要复杂得多。有多个级别，我不确定确切的数量。比如A被B监管，B被C监管，C被D监管等等

我假设只有 5 个或更多级别的监督。原始数据可能是这样的：

     Employee     Supervisor
        A             B
        C             B
        D             B
        B             V
        E             V
        F             E
        G             V
        V          (Blank which indicates no boss)
        H             A

BigQuery专家提供的代码如下：

#standardSQL
SELECT t.Supervisor,
  IF(t.Supervisor = t5.Supervisor, 
    STRUCT(Employee2 AS Employee1, NULL AS Employee2),
    STRUCT(t5.Supervisor AS Employee1, Employee2 AS Employee2)
  ).*
FROM (
  SELECT t1.Employee Supervisor,
    COALESCE(t4.Employee, t3.Employee, t2.Employee) Employee2
  FROM `project.dataset.table` t1
  LEFT JOIN `project.dataset.table` t2 ON t2.Supervisor = t1.Employee
  LEFT JOIN `project.dataset.table` t3 ON t3.Supervisor = t2.Employee
  LEFT JOIN `project.dataset.table` t4 ON t4.Supervisor = t3.Employee
  WHERE t1.Supervisor IS NULL
) t
LEFT JOIN `project.dataset.table` t5 ON t5.Employee = t.Employee2

结果变成了这样：

Row Supervisor  Employee1   Employee2    
1   V           B           A    
2   V           B           C    
3   V           B           D    
4   V           E           F    
5   V           G           null

但我们想要的是：

  Row Supervisor  Employee1   Employee2  Employee3  
    1   V           B           A          H
    2   V           B           C         Null
    3   V           B           D         Null
    4   V           E           F         Null
    5   V           G           null      Null

那么如果我想有更多的层次结构，如何更改代码呢？这意味着如果我想添加 employee3 或 4，我该如何编辑它？谢谢！

Answer 1

以下适用于 BigQuery 标准 SQL

#standardSQL
WITH e0 AS (
  SELECT Employee AS Supervisor FROM `project.dataset.table` WHERE Supervisor IS NULL
), e1 AS (
  SELECT e.Supervisor, Employee AS Employee1 
  FROM e0 e LEFT JOIN `project.dataset.table` t ON t.Supervisor = e.Supervisor
), e2 AS (
  SELECT e.Supervisor, Employee1, Employee AS Employee2
  FROM e1 e LEFT JOIN `project.dataset.table` t ON t.Supervisor = e.Employee1
), e3 AS (
  SELECT e.Supervisor, Employee1, Employee2, Employee AS Employee3
  FROM e2 e LEFT JOIN `project.dataset.table` t ON t.Supervisor = e.Employee2
)
SELECT * FROM e3

如果应用于您问题中的示例数据 - result/output 是

Row Supervisor  Employee1   Employee2   Employee3    
1   V           B           A           H    
2   V           B           C           null     
3   V           B           D           null     
4   V           E           F           null     
5   V           G           null        null

你可以很容易地在上面添加更多级别，如下所示（用 4、5、6、7 等相应的数字替换和）显然可以合理扩展

e<N> AS (
  SELECT e.Supervisor, Employee1, Employee2, Employee3, ... , Employee AS Employee<N>
  FROM e<N-1> e LEFT JOIN `project.dataset.table` t ON t.Supervisor = e.Employee<N-1>
)   
SELECT * FROM e<N>

例如

#standardSQL
WITH e0 AS (
  SELECT Employee AS Supervisor FROM `project.dataset.table` WHERE Supervisor IS NULL
), e1 AS (
  SELECT e.Supervisor, Employee AS Employee1 
  FROM e0 e LEFT JOIN `project.dataset.table` t ON t.Supervisor = e.Supervisor
), e2 AS (
  SELECT e.Supervisor, Employee1, Employee AS Employee2
  FROM e1 e LEFT JOIN `project.dataset.table` t ON t.Supervisor = e.Employee1
), e3 AS (
  SELECT e.Supervisor, Employee1, Employee2, Employee AS Employee3
  FROM e2 e LEFT JOIN `project.dataset.table` t ON t.Supervisor = e.Employee2
), e4 AS (
  SELECT e.Supervisor, Employee1, Employee2, Employee3, Employee AS Employee4
  FROM e3 e LEFT JOIN `project.dataset.table` t ON t.Supervisor = e.Employee3
), e5 AS (
  SELECT e.Supervisor, Employee1, Employee2, Employee3, Employee4, Employee AS Employee5
  FROM e4 e LEFT JOIN `project.dataset.table` t ON t.Supervisor = e.Employee4
)
SELECT * FROM e5

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