How Can I Calculate Cumulative Sums in MySQL?

Create cumulative sum column in MySQL

When processing data sets, it is often necessary to calculate the cumulative sum. In MySQL, this can be achieved in several ways.

Use related query

Related queries involve referencing data from other rows in the same query. To create a cumulative sum column using this method:

<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>

Using MySQL variables

MySQL variables can also be used for cumulative sum calculations. This involves declaring a variable and incrementing it in the query:

<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>

Note that cross joins (SELECT @running_total := 0) r are used to declare variables.

Notes

• These methods are MySQL specific, which means they may not work with other databases.
The
• ORDER BY clause is crucial, ensuring the correct order of calculations.
• MySQL variables have certain limitations, such as not being portable, and need to be used with care in more complex queries.

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