How Can a Recursive SQL Query Efficiently Group Products Based on Matching Relationships?

Recursive Query to Establish Product Groups in SQL Server

A common task in data analysis is to identify and group related entities. In this specific scenario, the goal is to process a table of product matches and store them in a separate table, where each row represents a product group. The product groups are determined by the "matching" relationship between products.

To achieve this, we can employ a recursive query using SQL Server's Common Table Expression (CTE). A recursive query allows a query to refer to its own output, enabling the implementation of complex joins and tree-like structures.

The CTE, named "CTE," first identifies the root nodes of each group by selecting the minimum product ID for each product that has no matching product. Then, it recursively joins with the matches table to identify the remaining products in each group.

The final query retrieves the data from the CTE and orders the results by the group ID. By specifying the OPTION(MAXRECURSION n) clause, we can control the maximum depth of recursion allowed, ensuring that the query doesn't enter an infinite loop.

Here's the SQL code for the recursive query:

;WITH CTE
AS
(
    SELECT DISTINCT
        M1.Product_ID Group_ID,
        M1.Product_ID
    FROM matches M1
        LEFT JOIN matches M2
            ON M1.Product_Id = M2.matching_Product_Id
    WHERE M2.matching_Product_Id IS NULL
    UNION ALL
    SELECT
        C.Group_ID,
        M.matching_Product_Id
    FROM CTE C
        JOIN matches M
            ON C.Product_ID = M.Product_ID
)
SELECT * FROM CTE ORDER BY Group_ID;

By employing this recursive query, you can effectively group products based on their matching relationships and store the results in a separate table for further analysis.

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