Google bigquery 如何在BigQuery标准SQL中获取数组的切片？

在BigQuery中，我有一个具有如下路径列的表：

ID .     | Path
---------+----------------------------------------
1        | foo/bar/baz
2        | foo/bar/quux/blat

我希望能够在正斜杠上拆分路径/并选择一个或多个路径部分，重新连接它们

在PostgreSQL中，这很简单：

select array_to_string((regexp_split_to_array(path, '/'))[1:3], '/')

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但是BigQuery似乎没有任何类型的范围偏移量或数组切片函数。

下面是BigQuery标准SQL

#standardSQL
SELECT id, path,
  (
    SELECT STRING_AGG(part, '/' ORDER BY index) 
    FROM UNNEST(SPLIT(path, '/')) part WITH OFFSET index 
    WHERE index BETWEEN 1 AND 3
  ) adjusted_path
FROM `project.dataset.table`  

您可以使用问题中的样本数据测试、播放上述内容，如下例所示

#standardSQL
WITH `project.dataset.table` AS (
  SELECT 1 id, 'foo/bar/baz/foo1/bar1/baz1/' path UNION ALL
  SELECT 2, 'foo/bar/quux/blat/foo2/bar2/quux2/blat2' 
)
SELECT id, path,
  (
    SELECT STRING_AGG(part, '/' ORDER BY index) 
    FROM UNNEST(SPLIT(path, '/')) part WITH OFFSET index 
    WHERE index BETWEEN 1 AND 3
  ) adjusted_path
FROM `project.dataset.table`   

#standardSQL
CREATE temp  FUNCTION ARRAY_SLICE(arr ARRAY<STRING>, start INT64, finish INT64) 
RETURNS ARRAY<STRING> AS (
  ARRAY(
    SELECT part FROM UNNEST(arr) part WITH OFFSET index 
    WHERE index BETWEEN start AND finish ORDER BY index
  )
);
SELECT id, path, 
  ARRAY_TO_STRING(ARRAY_SLICE(SPLIT(path, '/'), 1, 3), '/') adjusted_path
FROM `project.dataset.table`  

结果

Row     id      path                                        adjusted_path    
1       1       foo/bar/baz/foo1/bar1/baz1/                 bar/baz/foo1     
2       2       foo/bar/quux/blat/foo2/bar2/quux2/blat2     bar/quux/blat    

如果出于某种原因，您希望保持查询内联/类似于PostgreSQL数组中使用的查询，请参见下面的示例，将其命名为数组切片

#standardSQL
WITH `project.dataset.table` AS (
  SELECT 1 id, 'foo/bar/baz/foo1/bar1/baz1/' path UNION ALL
  SELECT 2, 'foo/bar/quux/blat/foo2/bar2/quux2/blat2' 
)
SELECT id, path,
  (
    SELECT STRING_AGG(part, '/' ORDER BY index) 
    FROM UNNEST(SPLIT(path, '/')) part WITH OFFSET index 
    WHERE index BETWEEN 1 AND 3
  ) adjusted_path
FROM `project.dataset.table`   

#standardSQL
CREATE temp  FUNCTION ARRAY_SLICE(arr ARRAY<STRING>, start INT64, finish INT64) 
RETURNS ARRAY<STRING> AS (
  ARRAY(
    SELECT part FROM UNNEST(arr) part WITH OFFSET index 
    WHERE index BETWEEN start AND finish ORDER BY index
  )
);
SELECT id, path, 
  ARRAY_TO_STRING(ARRAY_SLICE(SPLIT(path, '/'), 1, 3), '/') adjusted_path
FROM `project.dataset.table`  

显然，如果应用于相同的样本数据，您将得到相同的结果

#standardSQL
CREATE temp  FUNCTION ARRAY_SLICE(arr ARRAY<STRING>, start INT64, finish INT64) 
RETURNS ARRAY<STRING> AS (
  ARRAY(
    SELECT part FROM UNNEST(arr) part WITH OFFSET index 
    WHERE index BETWEEN start AND finish ORDER BY index
  )
);
WITH `project.dataset.table` AS (
  SELECT 1 id, 'foo/bar/baz/foo1/bar1/baz1/' path UNION ALL
  SELECT 2, 'foo/bar/quux/blat/foo2/bar2/quux2/blat2' 
)
SELECT id, path, 
  ARRAY_TO_STRING(ARRAY_SLICE(SPLIT(path, '/'), 1, 3), '/') adjusted_path
FROM `project.dataset.table`   

Row     id      path                                        adjusted_path    
1       1       foo/bar/baz/foo1/bar1/baz1/                 bar/baz/foo1     
2       2       foo/bar/quux/blat/foo2/bar2/quux2/blat2     bar/quux/blat    

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完美的非常感谢。很高兴它对你有用。请考虑接受回答，如果还没有投票，请：O