How to Efficiently Select MySQL Records by Day, Ignoring Time?

How to Select MySQL Records Based on Day Without Considering Time

When working with a table containing a datetime column, it is often necessary to retrieve records for a specific day, regardless of the time they occurred. However, using a simple date comparison can be inefficient and prevent index utilization.

The incorrect approach involves selecting records where the date function applied to the datetime column matches the desired day, such as:

SELECT *
FROM tablename
WHERE DATE(columnname) = '2012-12-25'

This query requires MySQL to calculate the date for every row, which can be computationally intensive and slow for large datasets. Additionally, the use of a calculation in the WHERE clause prevents the optimization of the query using an index on the datetime column.

Instead, a more efficient approach is to define a range of datetime values that represent the entire day, ensuring that it includes the beginning and end of the specific date. This is achieved using the BETWEEN clause:

SELECT *
FROM tablename
WHERE columnname BETWEEN '2012-12-25 00:00:00' AND '2012-12-25 23:59:59'

This modified query allows MySQL to utilize an index on the datetime column, significantly improving performance. It is important to note that this approach ensures that records from the entire day are selected, regardless of the time they occurred.

Note that in recent versions of MySQL, it is recommended to use the following syntax to avoid potential ambiguity:

SELECT *
FROM tablename
WHERE columnname >= '2012-12-25 00:00:00'
AND columnname < '2012-12-26 00:00:00'

By following these guidelines, you can efficiently select records based on the day without considering time in MySQL, ensuring optimal database performance.

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