How to Retrieve the First Row Where the Sum of Values Exceeds a Threshold in MySQL?

Using WHERE SUM() to Retrieve Specific Data in MySQL

MySQL provides the SUM() aggregation function to calculate the sum of values in a column. While SUM() is commonly used in SELECT queries to obtain aggregated results, it can also be employed in WHERE clauses with certain limitations.

In the given scenario, the objective is to retrieve the first row in a table where the sum of cash values from previous rows exceeds a specified threshold. Using "WHERE SUM(cash) > 500" in the WHERE clause will not yield the desired result because aggregates cannot be directly compared in this context.

To achieve the desired functionality, the HAVING clause should be used in conjunction with the GROUP BY clause. However, the HAVING clause requires a GROUP BY clause definition. Therefore, in this case, grouping would not be meaningful.

The solution is to utilize a nested subquery within the WHERE clause. This approach allows us to calculate the running total of cash values up to each row and then use that value in the comparison. The following query accomplishes this:

<code class="sql">SELECT y.id, y.cash
FROM (
  SELECT t.id,
         t.cash,
         (
           SELECT SUM(x.cash)
           FROM TABLE x
           WHERE x.id <= t.id
         ) AS running_total
  FROM TABLE t
  ORDER BY t.id
) y
WHERE y.running_total > 500
ORDER BY y.id
LIMIT 1;</code>

By referencing the column alias "running_total" in the WHERE clause, we can compare the running total to the specified threshold. The LIMIT clause ensures that only the first row meeting the criteria is returned.

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