Subquery to Display Sum of Column and Value of Column in a Date Range

As a technical blogger, I’ve encountered numerous SQL queries that involve aggregating data over time ranges. In this article, we’ll delve into the world of subqueries and explore how to use them to display both the sum of a column and its value within a specific date range.

Understanding Subqueries

A subquery is a query nested inside another query. It’s used to retrieve data from one or more tables based on conditions specified in the outer query. In this case, we’ll use a subquery to achieve our desired result.

Subqueries can be categorized into two types:

Correlated Subqueries: These queries are correlated with the outer query because they reference columns from the outer query.
Non-Correlated Subqueries: These queries do not reference any columns from the outer query and can be used to retrieve data without affecting the outer query.

The Challenge: Summing and Aggregating Data

In this scenario, we want to display the sum of a column (e.g., Balance) and its value within a specific date range. We also need to group our results by Company and Department. To accomplish this, we can use a combination of grouping, aggregation, and subqueries.

Using a Subquery with GROUP BY

To achieve our desired result using a subquery, we’ll follow these steps:

Identify the most recent date for each group: We’ll use a subquery to find the most recent date value for each group of Company and Department. This will allow us to accurately calculate the sum of the column.
Group by Company, Department, and date: We’ll then group our results by these three columns to obtain the desired output.

Example Query

Here’s an example query that demonstrates how to use a subquery with GROUP BY:

SELECT 
    Company,
    department,
    SUM(amount) AS Balance
FROM (
    SELECT MAX(date) AS date, Company, department, amount
    FROM GL_TABLE
    GROUP BY date
) AS subquery
WHERE  
    Company IN ('A', 'B', 'C') AND FY = 21 AND account = 'cash' AND date BETWEEN 
    1/1/2021 AND 1/31/2021
GROUP BY
    Company, department, date;

In this example:

The subquery finds the most recent date value for each group of Company and Department.
The outer query groups the results by these three columns.
We use SUM(amount) to calculate the total balance.

Using a Subquery with Correlated Calculations

When we need to perform correlated calculations (i.e., calculations that depend on values from the same row), we can’t simply nest another query. In this case, we’ll use a subquery with correlated calculations to achieve our desired result.

Example Query

Here’s an example query that demonstrates how to use a subquery with correlated calculations:

SELECT 
    Company,
    department,
    MAX(amount) AS most_recent_amount,
    SUM(amount) OVER (PARTITION BY Company, department ORDER BY date DESC) AS sum_amount
FROM (
    SELECT date, Company, department, amount,
           ROW_NUMBER() OVER (PARTITION BY Company, department ORDER BY date DESC) AS row_num
    FROM GL_TABLE
    WHERE Company IN ('A', 'B', 'C') AND FY = 21 AND account = 'cash' AND date BETWEEN 
        1/1/2021 AND 1/31/2021
) AS subquery
WHERE row_num = 1;

In this example:

The subquery finds the most recent date value for each group of Company and Department.
We use ROW_NUMBER() to assign a ranking to each row within the same partition.
In the outer query, we select only rows with row_num = 1, which corresponds to the most recent amount.

Best Practices

When working with subqueries:

Make sure to use correlated calculations carefully, as they can affect performance.
Avoid using subqueries that reference columns from the outer query; instead, use joined tables or aggregate functions like GROUP BY.
Optimize your queries by avoiding unnecessary joins and subqueries.

Conclusion

In this article, we explored how to use subqueries to display both the sum of a column and its value within a specific date range. We discussed correlated calculations and best practices for using subqueries effectively. By mastering subqueries and their various applications, you’ll be able to tackle complex SQL queries with confidence.

Additional Resources

For further learning:

Oracle’s official documentation on subqueries: https://docs.oracle.com/database/OracleQueryingData/subquery.html
W3Schools’ guide to subqueries: https://www.w3schools.com/sql/sql_subquery.asp

Last modified on 2023-08-29