How to Create Histograms in MySQL with Predefined Intervals?

Histogram Data Extraction in MySQL

MySQL natively provides limited support for binning data into predefined intervals for histogram plotting. However, this task can be achieved using a modified approach.

The SQL query you provided:

select total, count(total) from faults GROUP BY total;

generates an excessive number of rows. To group data into predefined bins, you can consider the following workaround:

ROUND(numeric_value, -2) AS bucket,

   COUNT(*)                    AS COUNT,
   RPAD('', LN(COUNT(*)), '*') AS bar

FROM my_table
GROUP BY bucket;

By adjusting the ROUNDing increment, you can define the bin sizes. For instance, ROUND(numeric_value, -2) groups data into buckets of 100 (-200 to -100, -100 to 0, etc.).

Modifying the offset in the ROUNDing operation ensures that the first bucket contains as many elements as subsequent buckets. For ROUND(numeric_value, -1), numeric_value in range [0,4] (5 elements) will be placed in the first bucket, while [5,14] (10 elements) in the second, [15,24] in the third, unless numeric_value is offset appropriately via ROUND(numeric_value - 5, -1).

As an example, the following query generates a histogram with logarithmic bar scaling:

SELECT ROUND(total, -2)    AS bucket,
       COUNT(*)                    AS COUNT,
       RPAD('', LN(COUNT(*)), '*') AS bar
FROM   faults
GROUP  BY bucket;

This approach provides a quick and adaptable method for creating histograms in MySQL, allowing for easy customization to specific use cases.

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