How Can I Efficiently Downsample Data from MySQL for Line Chart Creation?

Resampling Data for Line Chart Creation

When creating line charts from database values, it may be desirable to downsample the data to achieve a desired resolution. This can improve performance and reduce unnecessary data noise.

Selecting Every n-th Row from MySQL

To efficiently select every n-th row from a MySQL table, the following query can be used:

SELECT * 
FROM ( 
    SELECT 
        @row := @row +1 AS rownum, [column name] 
    FROM ( 
        SELECT @row :=0) r, [table name] 
    ) ranked 
WHERE rownum % [n] = 1 

In this query, the @row system variable is used to assign sequential row numbers to each row in the result set. The % operator then determines which rows to select based on the desired interval (n). For example, using [n] = 5 would select every 5th row.

Benefits

This approach offers several advantages:

• Efficiency: It uses the @row variable for efficient row numbering, avoiding the overhead of subqueries or row counts.
• Flexibility: It allows for easy customization of the sampling interval, making it applicable to various scenarios.
• Simplicity: The query is straightforward and easy to implement in most MySQL applications.

The above is the detailed content of How Can I Efficiently Downsample Data from MySQL for Line Chart Creation?. For more information, please follow other related articles on the PHP Chinese website!