How Can I Preserve Array Order When Joining Tables in PostgreSQL?

Preserving Ordering in PostgreSQL JOIN with Array Types: A Comprehensive Solution

The given database schema consists of two tables: items and some_chosen_data_in_order. The task at hand is to retrieve data from the items table for a specific row in the some_chosen_data_in_order table while preserving the order of elements in the array type field.

Ineffective Attempts:

Your initial attempts using JOIN and subqueries failed to maintain the element order in the array type field. These approaches do not consistently preserve the order in which the elements appear in the id_items array.

Effective Solution:

To resolve this issue, employ an alternative approach involving the unnest() function:

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

Explanation:

This query leverages the unnest() function to extract individual elements from the item_id array, effectively creating temporary rows for each element. Subsequently, we perform a LEFT JOIN with the items table to retrieve the desired data while maintaining the specified order.

Example:

Consider the some_chosen_data_in_order table containing a row with id_items as [1,2,3,2,3,5]. Executing the aforementioned query will return data related to the following items (in the specified order):

• Item with ID 1
• Item with ID 2
• Item with ID 3
• Item with ID 2
• Item with ID 3
• Item with ID 5

This solution ensures that the data retrieved from the items table aligns with the ordering of elements in the array type field of the some_chosen_data_in_order table.

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