postgresqlHow do I use the PostgreSQL UNNEST function?

The PostgreSQL UNNEST function allows you to expand an array into a set of rows. It takes an array as an input and returns a set of rows containing the elements of the array.

For example, if you have an array arr containing the elements [1, 2, 3], the following code will return three rows, each containing one element of the array:

SELECT unnest(arr)
FROM (SELECT ARRAY[1, 2, 3] AS arr) AS t;

unnest
-------
1
2
3
(3 rows)

The code above consists of two parts:

1. The SELECT statement, which uses the UNNEST function to expand the array arr into a set of rows.
2. The FROM clause, which defines the array arr as ARRAY[1, 2, 3].

For more information, please refer to the PostgreSQL documentation.

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