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Array Type

An `ARRAY` column stores fixed-sized arrays. All fields in the column must have the same length and the same underlying type. Arrays are typically used to store arrays of numbers, but can contain any uniform data type, including `ARRAY`, `LIST` and `STRUCT` types.

Arrays can be used to store vectors such as word embeddings or image embeddings.

To store variable-length lists, use the `LIST` type. See the data types overview for a comparison between nested data types.

> The `ARRAY` type in PostgreSQL allows variable-length fields. DuckDB's `ARRAY` type is fixed-length.

## Creating Arrays

Arrays can be created using the `array_value(expr, ...)` function.

Construct with the `array_value` function:

    SELECT array_value(1, 2, 3);

You can always implicitly cast an array to a list (and use list functions, like `list_extract`, `[i]`):

    SELECT array_value(1, 2, 3)[2];

You can cast from a list to an array (the dimensions have to match):

    SELECT [3, 2, 1]::INTEGER[3];

Arrays can be nested:

    SELECT array_value(array_value(1, 2), array_value(3, 4), array_value(5, 6));

Arrays can store structs:

    SELECT array_value({'a': 1, 'b': 2}, {'a': 3, 'b': 4});

## Defining an Array Field

Arrays can be created using the `⟨TYPE_NAME⟩[⟨LENGTH⟩]` syntax. For example, to create an array field for 3 integers, run:

    CREATE TABLE array_table (id INTEGER, arr INTEGER[3]);
    INSERT INTO array_table VALUES (10, [1, 2, 3]), (20, [4, 5, 6]);

## Retrieving Values from Arrays

Retrieving one or more values from an array can be accomplished using brackets and slicing notation, or through list functions like `list_extract` and `array_extract`. Using the example in Defining an Array Field.

The following queries for extracting the second element of an array are equivalent:

    SELECT id, arr[1] AS element FROM array_table;
    SELECT id, list_extract(arr, 1) AS element FROM array_table;
    SELECT id, array_extract(arr, 1) AS element FROM array_table;

id | element
--- | ---
10 | 1
20 | 4

Using the slicing notation returns a `LIST`:

    SELECT id, arr[1:2] AS elements FROM array_table;

id | elements
--- | ---
10 | [1, 2]
20 | [4, 5]

## Functions

All `LIST` functions work with the `ARRAY` type. Additionally, several `ARRAY`-native functions are also supported. See the `ARRAY` functions.

## Examples

Create sample data:

    CREATE TABLE x (i INTEGER, v FLOAT[3]);
    CREATE TABLE y (i INTEGER, v FLOAT[3]);
    INSERT INTO x VALUES (1, array_value(1.0::FLOAT, 2.0::FLOAT, 3.0::FLOAT));
    INSERT INTO y VALUES (1, array_value(2.0::FLOAT, 3.0::FLOAT, 4.0::FLOAT));

Compute cross product:

    SELECT array_cross_product(x.v, y.v)
    FROM x, y
    WHERE x.i = y.i;

Compute cosine similarity:

    SELECT array_cosine_similarity(x.v, y.v)
    FROM x, y
    WHERE x.i = y.i;

## Ordering

The ordering of `ARRAY` instances is defined using a lexicographical order. `NULL` values compare greater than all other values and are considered equal to each other.

## See Also

For more functions, see List Functions.

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