The intagg extension provides integer aggregation and enumeration functions, which are useful for working with integer arrays and creating sequences. This extension is particularly helpful when you need to aggregate integer values or generate enumerated lists. Your Nile database arrives with the intagg extension already enabled.

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Available Functions

The extension provides two main functions:
  1. int_array_aggregate(integer) - Aggregates integers into an array
  2. int_array_enum(integer[]) - Creates a set of integers from an array

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Integer Array Aggregation

Here’s how to use the integer aggregation function: 
-- Create a table to store student scores
CREATE TABLE scores (
    tenant_id uuid NOT NULL,
    student_id integer,
    subject text,
    score integer,
    PRIMARY KEY(tenant_id, student_id, subject)
);

INSERT INTO scores (tenant_id, student_id, subject, score) VALUES
    ('d1c06023-3421-4fbb-9dd1-c96e42d2fd02', 1, 'Math', 95),
    ('d1c06023-3421-4fbb-9dd1-c96e42d2fd02', 1, 'Science', 88),
    ('d1c06023-3421-4fbb-9dd1-c96e42d2fd02', 2, 'Math', 78),
    ('d1c06023-3421-4fbb-9dd1-c96e42d2fd02', 2, 'Science', 92);

-- Aggregate values into an array
SELECT int_array_aggregate(score) FROM scores;
-- Result: {95,88,78,92}

-- Get array of scores per student
SELECT student_id, int_array_aggregate(score) as scores
FROM scores
GROUP BY student_id;

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Integer Array Enumeration

The int_array_enum function unnesting aggregated arrays into rows. It is the opposite of int_array_aggregate. 
-- Convert array to rows
SELECT * FROM int_array_enum(ARRAY[1,2,3,4,5]);

-- Practical example: unnest aggregated scores
-- Pretend that scores are stored as an array of results per student, and we want to unnest them into rows
WITH aggregated_scores AS (
    SELECT student_id, int_array_aggregate(score) as scores
    FROM scores
    GROUP BY student_id
) 
SELECT student_id, unnested_score
FROM aggregated_scores,
     int_array_enum(scores) as unnested_score;

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Performance Considerations

  • The aggregation function is efficient for moderate-sized datasets
  • For very large datasets, consider using native PostgreSQL array_agg() function
  • The enumeration function is useful for small to medium-sized arrays

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Limitations

  • Works only with integer values
  • Not suitable for very large arrays due to memory constraints
  • The enumerated output maintains the order of the input array

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Alternative Approaches

For some use cases, you might want to consider these PostgreSQL native alternatives:
  1. array_agg() for general-purpose array aggregation
  2. generate_series() for generating sequences
  3. unnest() for array expansion
For more details, refer to the PostgreSQL documentation on aggregate functions. The official documentation for the intagg extension is here and includes a nice example of using the intagg functions to denormalize data and still be able to query it in a normalized way.