Materialize Documentation
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list_agg function

The list_agg(value, delimiter) aggregate function concatenates input values (including nulls) into a list. The input values to the aggregate can be filtered.

Syntax

list_agg ( value ORDER BY col_ref ASC DESC NULLS LAST NULLS FIRST , ) FILTER ( WHERE filter_clause )

Signatures

Parameter Type Description
value text The values to concatenate.

Return value

list_agg returns a list value.

This function always executes on the data from value as if it were sorted in ascending order before the function call. Any specified ordering is ignored. If you need to perform aggregation in a specific order, you must specify ORDER BY within the aggregate function call itself. Otherwise incoming rows are not guaranteed any order.

Details

Usage in dataflows

While list_agg is available in Materialize, materializing list_agg(values) is considered an incremental view maintenance anti-pattern. Any change to the data underlying the function call will require the function to be recomputed entirely, discarding the benefits of maintaining incremental updates.

Instead, we recommend that you materialize all components required for the list_agg function call and create a non-materialized view using list_agg on top of that. That pattern is illustrated in the following statements:

CREATE MATERIALIZED VIEW foo_view AS SELECT * FROM foo;
CREATE VIEW bar AS SELECT list_agg(foo_view.bar) FROM foo_view;

Examples

SELECT
    title,
    LIST_AGG (
        first_name || ' ' || last_name
        ORDER BY
            last_name
    ) actors
FROM
    film
GROUP BY
    title;