Using ROLLUP in MySQL for Conditional Aggregation on a Single Column

Learn how to implement the ROLLUP function in MySQL to create a super aggregate that only targets one specific column for accurate calculations.
---

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How do I use ROLLUP to create a super aggregate for only one column in mysql?

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Mastering ROLLUP in MySQL for Selective Aggregation

When working with MySQL, the ROLLUP feature can be incredibly useful for generating subtotals and grand totals for grouped data. However, a common issue arises when you want to perform a conditional aggregation that targets only specific columns while excluding others. In this post, we will dive into a practical scenario where you can apply ROLLUP to aggregate your results correctly, especially when your foreign key tables involve diverse currencies.

The Problem at Hand

Consider a database containing two tables: Business and Dividend. Your goal is to calculate year-to-date dividends while producing a grand total specifically for SGD (Singapore Dollar) dividends. However, the current setup mistakenly aggregates all dividend amounts, regardless of currency, resulting in incorrect totals in the final ROLLUP output.

Here’s a bird-eye view of the SQL structure we're dealing with:

[[See Video to Reveal this Text or Code Snippet]]

With these tables in place, you might run a query like this:

[[See Video to Reveal this Text or Code Snippet]]

The challenge here is ensuring the ROLLUP only sums the SGD_Year_To_Date_Dividends and returns a value of NULL or zero for the Year_To_Date_Dividends column in the grand total row.

A Step-by-Step Solution

To resolve this issue, we will need to adjust the calculation for the Year_To_Date_Dividends and SGD_Year_To_Date_Dividends as follows:

1. Update the Year-To-Date Dividends Calculation

Instead of simply summing all the values for Year_To_Date_Dividends, we will introduce an IF condition that outputs an empty string (or zero) when the row is for the grand total.

Here's the updated SQL code:

[[See Video to Reveal this Text or Code Snippet]]

2. Calculate SGD Year-To-Date Dividends

Next, we will enhance the calculation for SGD_Year_To_Date_Dividends. Use the ROUND function to deliver the result with two decimal points, enhancing clarity in your output. The new calculation should look like this:

[[See Video to Reveal this Text or Code Snippet]]

3. Final Query

Your final query will look like this:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By implementing the above adjustments, you can effectively use ROLLUP to achieve accurate aggregation for year-to-date dividends while ensuring that non-SGD totals do not affect the grand total calculation. This solution demonstrates the flexibility and power of MySQL's aggregation functions and reinforces the importance of precision in financial computations.

With these steps, your report now provides clear and correct insights into each company’s year-to-date dividends alongside the aggregated total in SGD.