How to Efficiently Calculate Cumulative Sums in MySQL?

Create cumulative sum column in MySQL

There are multiple ways to create a cumulative sum column in a MySQL table, each with its own advantages and considerations. A common approach is to use a correlated subquery:

<code class="language-sql">SELECT t.id,
       t.count,
       (SELECT SUM(x.count)
          FROM TABLE x
         WHERE x.id <= t.id) AS cumulative_sum
  FROM TABLE t
 ORDER BY t.id;</code>

This query calculates the cumulative sum of each row by relating the current row to all previous rows in the table, effectively aggregating the count values.

Alternatively, you can use MySQL variables:

<code class="language-sql">SELECT t.id,
       t.count,
       @running_total := @running_total + t.count AS cumulative_sum
  FROM TABLE t
  JOIN (SELECT @running_total := 0) r
 ORDER BY t.id;</code>

This method uses a cross connection with the inline view to initialize and update a variable @running_total that keeps track of the cumulative sum. Note that this method is MySQL specific and may not be portable to other databases.

Both methods require a ORDER BY clause to ensure that the result is consistent with the required cumulative sum calculation. When choosing the most appropriate method of creating a cumulative sum column in MySQL, consider the context and performance requirements of your application.

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