google-bigquery - BigQuery UDF 定义常量字典并匹配给定的函数参数

Question

定义映射的最佳方法是什么： Map(1 -> "One", 2 -> "Two") 并定义一个与上述函数匹配的函数？我正在考虑通过 Javascript 定义字典并在函数体中进行匹配。一个例子会很棒。谢谢

Answer 1

下面是 BigQuery 标准 SQL 的示例

#standardSQL
CREATE TEMP FUNCTION MAP(expr ANY TYPE, map ANY TYPE, `default` ANY TYPE ) AS (
  IFNULL((
    SELECT result 
    FROM (SELECT NULL AS search, NULL AS result UNION ALL SELECT * FROM UNNEST(map))
    WHERE search = expr), `default`)
);
WITH `project.dataset.table` AS (
  SELECT 1 id, 4 location_id UNION ALL
  SELECT 2, 2 UNION ALL
  SELECT 3, 5
)
SELECT id, location_id,
  MAP(location_id, 
    [ (1, 'Los Angeles'),
      (2, 'San Francisco'),
      (3, 'New York'),
      (4, 'Seattle')
    ], 'Non US') AS `Location`
FROM `project.dataset.table`   

结果

Row id  location_id Location     
1   1   4           Seattle  
2   2   2           San Francisco    
3   3   5           Non US