SQL：如何根据其值旋转行

Question

我要转换这个数据：

id  value
---------
1   v1=10
1   v2=20
1   v3=30
2   v1=40

看起来像这样：

id  v1     v2     v3
---------------------------
1   10     20     30
2   40     null   null

有什么解决办法吗？我想解决它 bigquery 的标准 sql.

Answer 1

SELECT
  id,
  MAX(IF(name = 'v1', value, NULL)) AS v1,
  MAX(IF(name = 'v2', value, NULL)) AS v2,
  MAX(IF(name = 'v3', value, NULL)) AS v3
FROM (
  SELECT
    SPLIT(value, '=')[OFFSET(0)] AS name,
    SPLIT(value, '=')[OFFSET(1)] AS value
  FROM dataset.table
)
GROUP BY id

Answer 2

以下几个选项 - 全部用于 BigQuery Standrad SQL

Option 1 - hardcoded pivoting

假设您事先知道要创建的列的数量和名称
在这种情况下，下面就是您需要的

#standardSQL
SELECT 
  id, 
  MAX(IF(key = 'v1', val, NULL)) v1,
  MAX(IF(key = 'v2', val, NULL)) v2,
  MAX(IF(key = 'v3', val, NULL)) v3
FROM `project.dataset.table`, 
UNNEST([STRUCT<key STRING, val STRING>(SPLIT(value,"=")[OFFSET(0)], SPLIT(value, "=")[OFFSET(1)])])
GROUP BY id

您可以使用您问题中的虚拟数据进行测试，如下所示

#standardSQL
WITH `project.dataset.table` AS (
  SELECT 1 id, 'v1=10' value UNION ALL
  SELECT 1, 'v2=20' UNION ALL
  SELECT 1, 'v3=30' UNION ALL
  SELECT 2, 'v1=40' 
)
SELECT 
  id, 
  MAX(IF(key = 'v1', val, NULL)) v1,
  MAX(IF(key = 'v2', val, NULL)) v2,
  MAX(IF(key = 'v3', val, NULL)) v3
FROM `project.dataset.table`, 
UNNEST([STRUCT<key STRING, val STRING>(SPLIT(value,"=")[OFFSET(0)], SPLIT(value, "=")[OFFSET(1)])])
GROUP BY id
-- ORDER BY id

结果符合预期：

Row     id      v1      v2      v3   
1       1       10      20      30   
2       2       40      null    null

Option 2 - dynamic pivoting

如果您不知道列的数量和名称 - 您首先需要生成类似于上述选项 #1 中的脚本

你应该运行下面得到它

#standardSQL
SELECT CONCAT('SELECT id, ', 
   STRING_AGG(
      CONCAT('MAX(IF(key = "', key, '", val, NULL)) as ', key)
   ) 
   ,' FROM `project.dataset.table`, UNNEST([STRUCT<key STRING, val STRING>(SPLIT(value, "=")[OFFSET(0)], SPLIT(value, "=")[OFFSET(1)])]) GROUP BY id')
FROM (
  SELECT SPLIT(value, '=')[OFFSET(0)] key 
  FROM `project.dataset.table`
  GROUP BY key
)

例如，如果你将运行它对抗同一个假人

#standardSQL
WITH `project.dataset.table` AS (
  SELECT 1 id, 'v1=10' value UNION ALL
  SELECT 1, 'v2=20' UNION ALL
  SELECT 1, 'v3=30' UNION ALL
  SELECT 2, 'v1=40' 
)
SELECT CONCAT('SELECT id, ', 
   STRING_AGG(
      CONCAT('MAX(IF(key = "', key, '", val, NULL)) as ', key)
   ) 
   ,' FROM `project.dataset.table`, UNNEST([STRUCT<key STRING, val STRING>(SPLIT(value, "=")[OFFSET(0)], SPLIT(value, "=")[OFFSET(1)])]) GROUP BY id')
FROM (
  SELECT SPLIT(value, '=')[OFFSET(0)] key 
  FROM `project.dataset.table`
  GROUP BY key
)

您将得到以下字符串

SELECT id, MAX(IF(key = "v1", val, NULL)) AS v1,MAX(IF(key = "v2", val, NULL)) AS v2,MAX(IF(key = "v3", val, NULL)) AS v3 FROM `project.dataset.table`, UNNEST([STRUCT<key STRING, val STRING>(SPLIT(value, "=")[OFFSET(0)], SPLIT(value, "=")[OFFSET(1)])]) GROUP BY id

那么，现在 - 如果你运行这个脚本针对你的虚拟数据

#standardSQL
WITH `project.dataset.table` AS (
  SELECT 1 id, 'v1=10' value UNION ALL
  SELECT 1, 'v2=20' UNION ALL
  SELECT 1, 'v3=30' UNION ALL
  SELECT 2, 'v1=40' 
)
SELECT id, MAX(IF(key = "v1", val, NULL)) AS v1,MAX(IF(key = "v2", val, NULL)) AS v2,MAX(IF(key = "v3", val, NULL)) AS v3 FROM `project.dataset.table`, UNNEST([STRUCT<key STRING, val STRING>(SPLIT(value, "=")[OFFSET(0)], SPLIT(value, "=")[OFFSET(1)])]) GROUP BY id

您将获得与选项 1 相同的结果 - 但不是 - 现在最终查询是为您动态生成的

Option 3 - flatten key - value vs. pivot

旋转很酷，但对于许多实际情况，下面的简单方法被发现非常有用，更适合处理

#standardSQL
WITH `project.dataset.table` AS (
  SELECT 1 id, 'v1=10' value UNION ALL
  SELECT 1, 'v2=20' UNION ALL
  SELECT 1, 'v3=30' UNION ALL
  SELECT 2, 'v1=40' 
)
SELECT 
  id, 
  SPLIT(value,"=")[OFFSET(0)] key, 
  SPLIT(value, "=")[OFFSET(1)] val
FROM `project.dataset.table`

这给出了普通键值扁平化结构

Row     id      key     val  
1       1       v1      10   
2       1       v2      20   
3       1       v3      30   
4       2       v1      40

SQL：如何根据其值旋转行

SQL: how to pivot rows based on its value

sql

google-bigquery

bigquery-standard-sql