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什么等价于BigQuery中的OTRANSLATE?

standard-sql teradata google-bigquery

Elliott Brossard · 技术社区 · 5 年前

我正在尝试将一个查询转换为在BigQuery中运行,它使用 OTRANSLATE function 来自Teradata。例如,

SELECT OTRANSLATE(text, 'ehlo', 'EHLO')
FROM (
  SELECT 'hello world' AS text UNION ALL
  SELECT 'elliott'
);

这将产生:

HELLO wOrLd
ELLiOtt

1 回复 | 直到 5 年前

Mikhail Berlyant 5 年前

另一种稍有不同的方法(BigQuery标准SQL)

#standardSQL
CREATE TEMP FUNCTION OTRANSLATE(text STRING, from_string STRING, to_string STRING) AS ((
  SELECT STRING_AGG(IFNULL(y, a), '' ORDER BY pos)
  FROM UNNEST(SPLIT(text, '')) a WITH OFFSET pos
  LEFT JOIN (
    SELECT x, y
    FROM UNNEST(SPLIT(from_string, '')) x WITH OFFSET
    JOIN UNNEST(SPLIT(to_string, '')) y WITH OFFSET
    USING(OFFSET)
  )
  ON a = x
));
WITH `project.dataset.table` AS (
  SELECT 'hello world' AS text UNION ALL
  SELECT 'elliott'
)
SELECT text, OTRANSLATE(text, 'ehlo', 'EHLO') as new_text
FROM `project.dataset.table`

有输出

Row     text            new_text     
1       hello world     HELLO wOrLd  
2       elliott         ELLiOtt

注意:以上版本假设from和to字符串的长度相等,from字符串中没有重复的字符

更新以跟踪BigQuery中该函数版本的“扩展期望”

#standardSQL
CREATE TEMP FUNCTION OTRANSLATE(text STRING, from_string STRING, to_string STRING) AS ((
  SELECT STRING_AGG(IFNULL(y, a), '' ORDER BY pos)
  FROM UNNEST(SPLIT(text, '')) a WITH OFFSET pos
  LEFT JOIN (
    SELECT x, ARRAY_AGG(IFNULL(y, '') ORDER BY OFFSET LIMIT 1)[OFFSET(0)] y
    FROM UNNEST(SPLIT(from_string, '')) x WITH OFFSET
    LEFT JOIN UNNEST(SPLIT(to_string, '')) y WITH OFFSET
    USING(OFFSET)
    GROUP BY x
  )
  ON a = x
));
SELECT -- text, OTRANSLATE(text, 'ehlo', 'EHLO') as new_text
  OTRANSLATE("hello world", "", "EHLO") AS empty_from, -- 'hello world'
  OTRANSLATE("hello world", "hello world1", "EHLO") AS larger_from_than_source, -- 'EHLLL'
  OTRANSLATE("hello world", "ehlo", "EHLO") AS equal_size_from_to, -- 'HELLO wOrLd'
  OTRANSLATE("hello world", "ehlo", "EH") AS larger_size_from, -- 'HE wrd'
  OTRANSLATE("hello world", "ehlo", "EHLOPQ") AS larger_size_to, -- 'hello world'
  OTRANSLATE("hello world", "ehlo", "") AS empty_to; -- 'wrd'

有结果的

Row empty_from  larger_from_than_source equal_size_from_to  larger_size_from    larger_size_to  empty_to     
1   hello world EHLLL                   HELLO wOrLd             HE wrd          HELLO wOrLd     wrd    
.

注意:这个函数的Teradata版本是递归的,所以当前的实现不是Teradata的OTRANSLATE的精确实现

使用说明
如果from_string中的第一个字符出现在源_string中,则它的所有出现都将替换为to_string中的第一个字符。对from_string中的所有字符和from_string中的所有字符重复此操作。替换是逐字符执行的,也就是说,第二个字符的替换是对第一个字符替换后的字符串执行的。

这可以很容易地用JS UDF实现,这很简单,我想我不会朝这个方向:o)

Elliott Brossard 5 年前

是的,可以使用字符串上的数组操作来完成此操作。以下是一个解决方案:

CREATE TEMP FUNCTION OTRANSLATE(s STRING, key STRING, value STRING) AS (
  (SELECT
     STRING_AGG(
       IFNULL(
         (SELECT value[OFFSET(
            SELECT o FROM UNNEST(SPLIT(key, '')) AS k WITH OFFSET o2
            WHERE k = c)]
         ),
         c),
       '' ORDER BY o1)
   FROM UNNEST(SPLIT(s, '')) AS c WITH OFFSET o1)
  )
);

SELECT OTRANSLATE(text, 'ehlo', 'EHLO')
FROM (
  SELECT 'hello world' AS text UNION ALL
  SELECT 'elliott'
);

这样做的目的是找到角色在 key value 弦。如果在字符串,我们最后得到一个空偏移量,因此 IFNULL 使其返回未映射的字符。然后我们再聚合成一个字符串,按字符偏移量排序。

编辑:这里有一个变体,它还处理键和值长度的差异:

CREATE TEMP FUNCTION otranslate(s STRING, key STRING, value STRING) AS (
  IF(LENGTH(key) < LENGTH(value) OR LENGTH(s) < LENGTH(key), s,
  (SELECT
     STRING_AGG(
       IFNULL(
         (SELECT ARRAY_CONCAT([c], SPLIT(value, ''))[SAFE_OFFSET((
            SELECT IFNULL(MIN(o2) + 1, 0) FROM UNNEST(SPLIT(key, '')) AS k WITH OFFSET o2
            WHERE k = c))]
         ),
         ''),
       '' ORDER BY o1)
   FROM UNNEST(SPLIT(s, '')) AS c WITH OFFSET o1
  ))
);
SELECT
  otranslate("hello world", "", "EHLO") AS empty_from, -- 'hello world'
  otranslate("hello world", "hello world1", "EHLO") AS larger_from_than_source, -- 'hello world'
  otranslate("hello world", "ehlo", "EHLO") AS equal_size_from_to, -- 'HELLO wOrLd'
  otranslate("hello world", "ehlo", "EH") AS larger_size_from, -- 'HE wrd'
  otranslate("hello world", "ehlo", "EHLOPQ") AS larger_size_to, -- 'hello world'
  otranslate("hello world", "ehlo", "") AS empty_to; -- 'wrd'