Map, filter & aggregate with TRANSFORM()

The TRANSFORM() function allows you to treat arrays of rows like mini tables and manipulate them using familiar FeatureQL syntax.

Here's the general structure:

TRANSFORM(
    base
    WITH (
        WITH [...internal field definitions]
        SELECT [...fields to return including group bys]
        WHERE [...final filter, equivalent of having]
        ORDER BY [...sort expressions]
        OFFSET [...skip rows]
        LIMIT [...max rows]
    )
    IMPORTING [...imported features]
)

sql

You can:

SELECT ...: generate new fields from existing fields
WHERE ...: filter post aggregation
... FILTER (WHERE ...) GROUP BY ...: aggregate filtered data
ORDER BY ...: sort data
LIMIT ...: limit the number of rows returned
OFFSET ...: skip the first n rows

The transformation query must be self contained.

Therefore, you cannot perform the following operations inside the TRANSFORM() query:

Reference data outside of the array of rows,
Join with external tables or fields, so no EXTEND() on fields,
Nest other TRANSFORM().

You need to perform these operations from the outside of the TRANSFORM() query. See examples here.

Example usage

Here are examples demonstrating practical cases:

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Last update at: 2025/12/05 16:03:14

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Example usage