How Can I Dynamically Pivot Data in BigQuery Using the PIVOT Function?

PIVOT Function in BigQuery: Handling Dynamic Quarter Values

BigQuery's recently introduced PIVOT function offers a convenient way to transform data into a tabular format, pivoting rows on specified columns. However, in real-world scenarios, we often encounter situations where the pivot column values (e.g., quarters) are unknown beforehand.

To address this challenge, let's consider the following query:

SELECT * FROM
  (SELECT * FROM Produce)
  PIVOT(SUM(sales) FOR quarter in (select distinct quarter from Produce))

While this query attempts to pivot the Produce table on the quarter column dynamically, it fails to produce the desired results. The missing ingredient is the need to dynamically build the PIVOT clause.

The solution lies in using SQL's execute immediate function to execute a dynamically generated query. Here's an improved query:

execute immediate (             
select '''select * from (select * from `project.dataset.Produce`)
  pivot(sum(sales) for quarter in ("''' ||  string_agg(quarter, '", "')  || '''"))
'''
from (select distinct quarter from `project.dataset.Produce` order by quarter) 
);

This query performs the following steps:

1. Creates a string containing a modified PIVOT query. The quarter values are dynamically generated using string_agg.
2. Executes the modified query to retrieve the desired pivot table.
3. Specifies an ordering on the distinct quarter values to ensure the columns appear in a consistent order.

By leveraging SQL's flexibility, we can overcome the limitation of static pivot columns and handle dynamic values seamlessly.

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