TOPN_WEIGHTED

Description

The TOPN_WEIGHTED function returns the N most frequent values in the specified column with weighted counting. Unlike the regular TOPN function, TOPN_WEIGHTED allows adjusting the importance of values through weights.

Syntax

TOPN_WEIGHTED(<expr>, <weight>, <top_num> [, <space_expand_rate>])

Parameters

Parameter	Description
<expr>	The column or expression to be counted. Supported types: TinyInt, SmallInt, Integer, BigInt, LargeInt, Float, Double, Decimal, Date, Datetime, IPV4, IPV6, String.
<weight>	The column or expression used to adjust the weight. Supported type: Double.
<top_num>	The number of most frequent values to return. Must be a positive integer. Supported type: Integer.
<space_expand_rate>	Optional. Sets the number of counters used in the Space-Saving algorithm: counter_numbers = top_num * space_expand_rate. The larger the value, the more accurate the result. Default is 50. Supported type: Integer.

Return Value

Returns an array containing the N values with the highest weighted counts. If there is no valid data in the group, returns NULL.

Example

-- setup
CREATE TABLE product_sales (
    product_id INT,
    sale_amount DECIMAL(10,2),
    sale_date DATE
) DISTRIBUTED BY HASH(product_id)
PROPERTIES (
    "replication_num" = "1"
);
INSERT INTO product_sales VALUES
(1, 100.00, '2024-01-01'),
(2, 50.00, '2024-01-01'),
(1, 150.00, '2024-01-01'),
(3, 75.00, '2024-01-01'),
(1, 200.00, '2024-01-01'),
(2, 80.00, '2024-01-01'),
(1, 120.00, '2024-01-01'),
(4, 90.00, '2024-01-01');

SELECT TOPN_WEIGHTED(product_id, sale_amount, 3) as top_products
FROM product_sales;

Find the top 3 products by sales amount (weighted).

+--------------+
| top_products |
+--------------+
| [1, 2, 4]    |
+--------------+

SELECT TOPN_WEIGHTED(product_id, sale_amount, 3) as top_products
FROM product_sales where product_id is null;

Find the top 3 products by sales amount (weighted).

+--------------+
| top_products |
+--------------+
| NULL         |
+--------------+