How to Preserve Array Element Order When Joining PostgreSQL Tables with Array Fields?

Implementing PostgreSQL JOIN with Array Type and Preserving Array Element Order

Problem:
Retrieve data from the items table, maintaining the order of elements in the array type field in the some_chosen_data_in_order table for a specific row.

Attempt #1: JOIN

SELECT I.* FROM items AS I
JOIN some_chosen_data_in_order AS S ON I.id = ANY(S.id_items)
WHERE S.id = ?

Attempt #2: Subquery

SELECT I.* FROM items AS I
WHERE I.id = ANY
(ARRAY[SELECT S.id_items FROM some_chosen_data_in_order WHERE id = ?])

Neither of these approaches preserve the order of elements in the array.

Solution:

SELECT t.*
FROM unnest(ARRAY[1,2,3,2,3,5]) item_id
LEFT JOIN items t on t.id=item_id

This query unnests the array into individual rows, preserving the element order. It then joins the resulting items with the items table based on the id field.

Example:

The above query will return the following result:

Explanation:

The unnest function unpacks the array into a table with one row per element. The LEFT JOIN ensures that all items from the array are returned, including those that do not have corresponding rows in the items table.

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