Google Bigquery Legacy SQL - 如何 return 如果没有结果 return 为 null 或零？

Question

假设我有以下 table

month    region   revenue   
------  -------- ---------- 
 jan     north      100
 feb     north      150
 mar     north      250

我怎样才能查询上面的 table 以获得以下结果？:

month    region   revenue   
------  -------- ---------- 
 jan     north      100
 feb     north      150
 mar     north      250
 apr     north       0
 may     north       0
 jun     north       0

0 可以为空，反之亦然。本质上是尝试将 empty/null 字段添加到我的查询中（在本例中为 apr、may、jun 行）。任何帮助将不胜感激

谢谢

Answer 1

一个选项 - 运行 a LEFT/RIGHT JOIN 与您要查看的值列表。

让我们从缺少 nulls/zeros:

的查询开始

#standardSQL
SELECT year, SUM(number) c
FROM `bigquery-public-data.usa_names.usa_1910_current`
WHERE name='Felipe'
AND year>2014
GROUP BY year 
ORDER BY year

如果我们想为 2015 年之前的值取 0：

SELECT b.year, IFNULL(c, 0) c
FROM (
  SELECT year, SUM(number) c
  FROM `bigquery-public-data.usa_names.usa_1910_current`
  WHERE name='Felipe'
  AND year>2014
  GROUP BY year 
) a
RIGHT JOIN (
  SELECT year FROM UNNEST(GENERATE_ARRAY(2012, 2016)) year
) b
ON a.year=b.year
ORDER BY year

相关子查询也可以挽救局面：

SELECT year, (
  SELECT IFNULL(SUM(number), 0) 
  FROM `bigquery-public-data.usa_names.usa_1910_current` a
  WHERE name='Felipe'
  AND year>2014
  AND a.year=b.year
) c
FROM (SELECT year FROM UNNEST(GENERATE_ARRAY(2012, 2016)) year) b
ORDER BY year

Answer 2

以下适用于旧版 BigQuery SQL，但请注意 - 强烈建议 BigQuery 团队迁移到 BigQuery Standard SQL

下面的例子应该会给你一个想法

#legacySQL
SELECT 
  months.month_abr AS month_abr, 
  regions.region AS region, 
  COALESCE(revenues.revenue, 0) revenue
FROM months
CROSS JOIN (
  SELECT region FROM revenues
) regions
LEFT JOIN revenues
ON months.month_abr = revenues.month_abr
AND regions.region = revenues.region
-- ORDER BY regions.region, months.month_number

其中 revenues 是带有收入数据的原始 table，month 是带有月份列表的 table（或者您可以使用子查询，如下例所示）

您可以使用下面的示例使用问题中的虚拟数据测试/播放上面的内容

#legacySQL
SELECT 
  months.month_abr AS month_abr, 
  regions.region AS region, 
  COALESCE(revenues.revenue, 0) revenue
FROM (
  SELECT month_number, month_abr FROM 
  (SELECT 1 month_number, 'jan' month_abr),
  (SELECT 2 month_number, 'feb' month_abr),
  (SELECT 3 month_number, 'mar' month_abr),
  (SELECT 4 month_number, 'apr' month_abr),
  (SELECT 5 month_number, 'may' month_abr),
  (SELECT 6 month_number, 'jun' month_abr)  
) AS months
CROSS JOIN (
  SELECT region FROM (
    SELECT region FROM 
    (SELECT 'jan' month_abr, 'north' region, 100 revenue),
    (SELECT 'feb' month_abr, 'north' region, 150 revenue),
    (SELECT 'mar' month_abr, 'north' region, 250 revenue)
  ) GROUP BY region
) regions
LEFT JOIN (
  SELECT month_abr, region, revenue FROM 
  (SELECT 'jan' month_abr, 'north' region, 100 revenue),
  (SELECT 'feb' month_abr, 'north' region, 150 revenue),
  (SELECT 'mar' month_abr, 'north' region, 250 revenue)
) AS revenues
ON months.month_abr = revenues.month_abr
AND regions.region = revenues.region
ORDER BY regions.region, months.month_number

结果如下

Row month_abr   region  revenue  
1   jan         north   100  
2   feb         north   150  
3   mar         north   250  
4   apr         north   0    
5   may         north   0    
6   jun         north   0

最后 - 下面是 BigQuery Standard SQL

#standardSQL
WITH regions AS (
  SELECT DISTINCT region FROM revenues
), months AS (
SELECT EXTRACT(MONTH FROM month) month_number,
  LOWER(FORMAT_DATE('%b', month)) month_abr
  FROM UNNEST(GENERATE_DATE_ARRAY(DATE '2010-01-01', DATE '2010-12-01', INTERVAL 1 MONTH)) month
)
SELECT month_abr, region, COALESCE(revenues.revenue, 0) revenue
FROM months
CROSS JOIN regions
LEFT JOIN revenues
USING(month_abr, region)
ORDER BY region, month_number

你可以测试，使用你问题中的虚拟数据来玩这个

#standardSQL
WITH revenues AS (
  SELECT 'jan' month_abr, 'north' region, 100 revenue UNION ALL
  SELECT 'feb', 'north', 150 UNION ALL
  SELECT 'mar', 'north', 250 
), regions AS (
  SELECT DISTINCT region FROM revenues
), months AS (
SELECT EXTRACT(MONTH FROM month) month_number,
  LOWER(FORMAT_DATE('%b', month)) month_abr
  FROM UNNEST(GENERATE_DATE_ARRAY(DATE '2010-01-01', DATE '2010-12-01', INTERVAL 1 MONTH)) month
)
SELECT month_abr, region, COALESCE(revenues.revenue, 0) revenue
FROM months
CROSS JOIN regions
LEFT JOIN revenues
USING(month_abr, region)
ORDER BY region, month_number

您应该能够将以上应用到您的实际用例中

Google Bigquery Legacy SQL - 如何 return 如果没有结果 return 为 null 或零？

Google Bigquery Legacy SQL - How to return a null or zero if no results returned?

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