How Can I Calculate Cumulative Sums in MySQL Without Built-in Analytic Functions?

Cumulative Sum Calculation in MySQL

This inquiry addresses the issue of computing cumulative sums for a set of rows in MySQL, where the desired output includes columns for ID, Day, Hour, Amount, and Cumulative Total. The initial query, which produces the raw data, involves complex operations like joins and unions.

MySQL's Limitations and Alternative Approaches

MySQL lacks built-in analytic functions that directly provide cumulative sum calculations. However, there are two potential approaches:

Correlated Subquery Method

This approach employs a subquery for each row to determine the subtotal, which can be costly for large datasets and complex queries.

User Variable Control Break Processing

This method utilizes MySQL user variables to emulate control break processing and accumulate cumulative sums based on row sequence. Here's a detailed implementation:

1. Initialization: An inline view initializes user variables for ID and Day to null and cumulative total to zero.
2. Wrapper Query: The original query is wrapped in parentheses and assigned an alias to introduce an ordering clause.
3. Cumulative Sum Logic: The outer query compares ID and Day values of adjacent rows. If they match, it adds the current amount to the cumulative total stored in the user variable. If they differ, it resets the cumulative total to the current amount.
4. User Variable Update: After calculating the cumulative total, the user variables are updated with the current row's ID and Day values, preparing for the next row processing.

By incorporating these steps, MySQL can effectively emulate cumulative sum calculations even in the absence of standard analytic functions.

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