Retrieving the Latest Record for Each ID from Two Tables in Oracle SQL

As a technical blogger, I often find myself exploring various databases and querying techniques. Recently, I came across a Stack Overflow question that caught my attention - “how to pull latest record for each ID from 2 tables in Oracle SQL.” In this blog post, we will delve into the details of how to achieve this using Oracle SQL.

Understanding the Problem

The problem at hand involves two tables: Product and Sold_Product. The Product table contains information about products, including their IDs, names, and rack numbers. The Sold_Product table stores data about sold products, including product codes, sale dates, and corresponding product IDs.

We need to retrieve the latest sold date for each unique product ID from both tables and display the corresponding product code, name, and maximum sold date.

Table Structure

Here’s a representation of the two tables:

Product Table

Example Data:

+---------+-----------------+-------+
| product_id| product_name  | rack_no |
+---------+-----------------+-------+
| 380      | Television    | 5     |
| 344      | Refridgerator | 4     |
| 333      | Air Conditioner| 6     |
+---------+-----------------+-------+

Sold_Product Table

Example Data:

+------------+----------+---------+
| product_code| sold_date| product_id|
+------------+----------+---------+
| 46077862546| 18/08/21| 380      |
| 41237862546| 18/08/21| 300      |
| 41237862789| 06/08/21| 356      |
+------------+----------+---------+

Solution Overview

To solve this problem, we will use a combination of the MAX function, subqueries, and joins to retrieve the desired data.

Step 1: Identify the Maximum Sold Date for Each Product ID

First, let’s find the maximum sold date for each product ID from the Sold_Product table. We can do this using the following SQL query:

SELECT prCode, prid, MAX(soldDate) AS MaxDate 
FROM Sold_Product 
GROUP BY prid;

This query groups the data by product_id and calculates the maximum sold_date for each group.

Step 2: Join the Product Table with the Subquery

Next, we need to join the Product table with the subquery from Step 1. We can use an inner join to match the product_id columns between the two tables. However, since the Sold_Product table does not have a product_name column, we will only include the product_id in our join.

SELECT p.product_id, p.product_name, ap.MaxDate 
FROM Product p, (
  SELECT prCode, prid, MAX(soldDate) AS MaxDate 
  FROM Sold_Product 
  GROUP BY prid)
ap
WHERE p.product_id = ap.prid;

This query joins the Product table with a subquery that returns the maximum sold date for each product ID. The join is performed on the product_id column, which matches between both tables.

Step 3: Filter Results to Include Only Unique Product IDs

Finally, we want to ensure that our results only include unique product IDs. Since the Product table has a single entry for each product ID, we can use the IN operator to filter out any duplicate product IDs.

SELECT p.product_id, p.product_name, ap.MaxDate 
FROM Product p, (
  SELECT prCode, prid, MAX(soldDate) AS MaxDate 
  FROM Sold_Product 
  GROUP BY prid)
ap
WHERE p.product_id = ap.prid AND p.product_id IN (SELECT product_id FROM Product);

However, the above query is not necessary as we already have a unique product_id in the Product table.

Step 4: Finalize the Query

Combining all the steps, our final query looks like this:

SELECT p.product_id, p.product_name, ap.MaxDate 
FROM Product p, (
  SELECT prCode, prid, MAX(soldDate) AS MaxDate 
  FROM Sold_Product 
  GROUP BY prid)
ap
WHERE p.product_id = ap.prid;

This query retrieves the desired data by joining the Product table with a subquery that returns the maximum sold date for each product ID.

Best Practices and Variations

Here are some additional best practices and variations to consider:

• Use indexes: Indexes can significantly improve query performance, especially when dealing with large datasets.
• Avoid using SELECT *: Instead, specify only the necessary columns to reduce the amount of data being transferred.
• Consider using Common Table Expressions (CTEs): CTEs can simplify complex queries and make them easier to maintain.

Conclusion

In this blog post, we explored how to retrieve the latest record for each ID from two tables in Oracle SQL. We discussed the use of subqueries, joins, and filters to achieve our goal. By following these steps and best practices, you can efficiently retrieve the desired data from your database.

Last modified on 2024-09-20