Recursive Query in PostgreSQL for Hierarchical Data

To perform a recursive query in PostgreSQL for a hierarchical data problem, you can use a common table expression (CTE) with the WITH RECURSIVE statement.

Here is a succinct SQL command to solve the problem:

WITH RECURSIVE cte AS (
    -- Base case: Select the root node(s) you want to start with
    SELECT *
    FROM your_table
    WHERE 
    
    UNION
    
    -- Recursive case: Join the CTE with the table to retrieve child nodes recursively
    SELECT t.*
    FROM your_table t
    JOIN cte ON t.parent_id = cte.node_id
)
-- Final query: Perform any additional operations on the hierarchical data
SELECT *
FROM cte;

The steps involved in constructing this recursive query are as follows:

1. Start with a WITH RECURSIVE statement and define a common table expression (CTE) named cte.
2. In the CTE, specify the base case by selecting the root node(s) you want to start with. Use the your_table to represent your actual table name.
3. Use the UNION operator to combine the base case with the recursive case.
4. In the recursive case, join the CTE with the table (your_table) using the appropriate join condition (e.g., parent_id = node_id). This will retrieve the child nodes recursively.
5. Perform any additional operations on the hierarchical data using the CTE. You can specify your desired columns, apply filters, or perform aggregations.
6. Finally, outside the CTE, select the desired columns from the CTE to retrieve the hierarchical data.

Remember to replace <root_node_condition> with the appropriate condition to select the root node(s) based on your specific problem.

This recursive query is a powerful tool for working with hierarchical data in PostgreSQL and can be used for various purposes such as navigating tree structures or calculating hierarchical aggregations.