使用 Bigquery 中的 Select 从行数据动态创建列

2021-12-30 00:00:00 sql google-bigquery mysql dynamic-sql

背景

我想动态地重命名我在 sql select 语句中的 case 语句.

I want to rename my case statement in sql select statement dynamically.

例如:

SELECT (case when id= x.id then x.sums end) x.idas (select id,count(*) sums from tablegroup by id) x

我想要的输出是创建的列列表，标签与id"列不同.

what i want the output is list of columns created ,with Labels as distinct id's from "id" column.

但是，这个变量 x.id 不是动态输出值，而是我输出单列 x.id.

However,this variable x.id is not dynamically outputing values,rather i get output a single column x.id.

例如:

表中的列...

1----x1---x2

1----x1---x2

2----x2----x3

2----x2----x3

3----x4----x5

3----x4----x5

运行查询后预期的列...

columns expected after running query...

但实际的 o/p 列是::

but actual o/p column is::

查询任何想法，如何使用选择查询动态生成列，如果我错了，请纠正我.

Query Any ideas,how to generate columns dynamically using select query,please correct me ,if i am wrong.

推荐答案

以下是 BigQuery！

Below is for BigQuery!

请注意:您对输出列名称的期望不正确！
列名不能以数字开头 - 所以在下面的例子中 - 我将使用 id_1、id_2 和 id_3 而不是 1、2 和 3

Please note: your expectations about output column names are not correct!
Column name cannot start with digit - so in below example - i will be using id_1, id_2 and id_3 instead of 1, 2 and 3 

SELECT
  SUM(CASE WHEN id = 1 THEN 1 END) AS id_1,
  SUM(CASE WHEN id = 2 THEN 1 END) AS id_2,
  SUM(CASE WHEN id = 3 THEN 1 END) AS id_3
FROM YourTable

上面的例子假设你事先知道你的 ID 并且它们很少，所以为每个 ID 手动编写几行 SUM(...) 并不是什么大问题

Above example assumes you know in advance your IDs and there are very few of them so it is not a big deal to write manually few numbers of lines with SUM(...) for each id

如果不是这种情况 - 您可以首先通过运行下面的查询以编程方式生成上面的查询

If this is not a case - you can first generate above query programmatically by running below query 

SELECT 'SELECT ' + 
   GROUP_CONCAT_UNQUOTED(
      'SUM(CASE WHEN id = ' + STRING(id) + ' THEN 1 END) AS id_' + STRING(id)
   ) 
   + ' FROM YourTable'
FROM (
  SELECT id FROM (
    SELECT * FROM YourTable GROUP BY id ORDER BY id
)

结果 - 你会得到如下所示的字符串

as a result - you will get string like below 

SELECT SUM(CASE WHEN id = 1 THEN 1 END) AS id_1,SUM(CASE WHEN id = 2 THEN 1 END) AS id_2,SUM(CASE WHEN id = 3 THEN 1 END) AS id_3 FROM YourTable

所以，现在只需将其复制并粘贴到查询编辑器中并运行它

So, now just copy it and paste into Query Editor and run it

你可以在这里看到类似的例子 - https://stackoverflow.com/a/36623258/5221944

you can see similar example here - https://stackoverflow.com/a/36623258/5221944

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