How Can I Create Histograms with Custom Bin Sizes in MySQL?

Creating Histograms with Custom Bin Sizes in MySQL

In MySQL, extracting data for histogram plots often involves grouping data based on predefined bin sizes. While basic grouping can be achieved using the GROUP BY clause, specifying customized bin sizes presents a challenge. However, a simple workaround can help you achieve this objective.

Consider the following SQL query:

<code class="sql">select total, count(total) from faults GROUP BY total;</code>

This query produces detailed data, but having numerous rows can be overwhelming. To group the data into predefined bins directly in SQL, you can leverage a straightforward approach:

<code class="sql">SELECT ROUND(numeric_value, -2)    AS bucket,
       COUNT(*)                    AS count,
       RPAD('', LN(COUNT(*)), '*') AS bar
FROM   my_table
GROUP  BY bucket;</code>

Adjusting the rounding increment within the ROUND function allows you to customize the bin size. For example, ROUND(numeric_value, -1) creates bins of size 10. By modifying the rounding increment and the initial offset, you can tailor the bin sizes to your specific requirements.

The trick here is using the ROUND function with an appropriate offset to ensure each bin contains approximately the same number of elements. Alternatively, TRUNCATE can be used instead of ROUND.

This solution provides a convenient and flexible way to create histograms with custom bin sizes in MySQL. For more advanced histogram creation techniques, consider exploring CASE statements or other complex logic for enhanced flexibility.

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