How to Efficiently Generate a Cumulative Sum Column in MySQL?

Calculating Cumulative Sums in MySQL: Two Approaches

This guide details two effective methods for generating cumulative sum columns within MySQL databases.

Method 1: Utilizing Correlated Subqueries

This approach employs a correlated subquery to compute the cumulative sum:

<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>

The correlated subquery, embedded within the AS clause, dynamically calculates the cumulative sum for each row. It sums the count values from the beginning of the table up to and including the current row's id.

Method 2: Leveraging MySQL Variables

MySQL variables offer an alternative method for cumulative sum calculations:

<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 initializes a MySQL variable, @running_total, to 0 using a cross join. As the query iterates through each row in TABLE t, @running_total accumulates the count values, producing the cumulative sum.

Important Considerations:

• The use of MySQL variables is database-specific and may not be compatible with other database systems.
• Both methods necessitate an ORDER BY clause to ensure accurate cumulative sum calculation. The order of rows dictates the summation sequence.

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