How Can I Dynamically Pivot Data in BigQuery When Pivot Column Values Are Unknown?

Utilizing BigQuery's PIVOT Function Dynamically

BigQuery's latest addition, the PIVOT function, has garnered considerable attention for its ability to transform data into a more pivot-table-like format. However, when faced with scenarios where the pivot column values are not known in advance, conventional methods may prove ineffective.

In such cases, a dynamic approach using string concatenation can bypass this limitation. By dynamically generating the pivot query based on the distinct values of the quarter column, we can effectively handle any number of unknown pivot values.

Code Snippet

The following code snippet exemplifies this dynamic approach:

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) 
);

How it Works

1. EXECUTE IMMEDIATE: This statement dynamically executes the generated query string.

2. Query Generation:

   • select '''select * from (select * from project.dataset.Produce): Fetch the data from the Produce table as a subquery.
   • pivot(sum(sales) for quarter in ("''': Begin the PIVOT operation, specifying the sum of sales for the quarter column.
   • string_agg(quarter, '", "'): Dynamically concatenate the distinct quarter values into a comma-separated string enclosed with double quotes to serve as the pivot column list.
   • "'''")): Complete the PIVOT clause.

3. Subquery:

   • (select distinct quarter from project.dataset.Produce order by quarter): Retrieve the distinct quarter values in ascending order to ensure proper pivot column ordering.

Advantages

This dynamic approach offers several benefits:

• Scalability: It seamlessly handles an arbitrary number of pivot column values, providing flexibility and ease of use.
• Conciseness: String concatenation allows for the construction of the PIVOT query in a single statement, enhancing code clarity.

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