How to Accurately Calculate the Difference in Years Between Two Dates in MySQL?

Precisely Determining the Year Difference Between Dates in MySQL

Challenge:

Accurately calculate the difference in years between two dates within a MySQL database, correctly handling leap years and ensuring consistent results.

MySQL Solution:

<code class="language-sql">YEAR(date1) - YEAR(date2) - (DATE_FORMAT(date1, '%m%d') < DATE_FORMAT(date2, '%m%d'))</code>

Detailed Breakdown:

• YEAR(date1) - YEAR(date2): Calculates the raw difference in years between the two input dates.
• (DATE_FORMAT(date1, '%m%d') < DATE_FORMAT(date2, '%m%d')): This part checks if the month and day of date1 precede those of date2. If true, it means date1 falls earlier in the year than date2, even if the year difference is already calculated.

The boolean result (TRUE/FALSE) of the comparison is implicitly converted to an integer (1 for TRUE, 0 for FALSE). This integer is then subtracted from the initial year difference, ensuring accurate year counting.

Illustrative Examples:

The following table demonstrates the method's accuracy:

<code>+------------+------------+------------+
| date1      | date2      | diff_years |
+------------+------------+------------+
| 2011-07-20 | 2011-07-18 |          0 |
| 2011-07-20 | 2010-07-20 |          1 |
| 2011-06-15 | 2008-04-11 |          3 |
| 2011-06-11 | 2001-10-11 |          9 |
| 2007-07-20 | 2004-07-20 |          3 |
+------------+------------+------------+</code>

Summary:

This concise MySQL expression provides a reliable and precise method for calculating the difference in years between two dates, meticulously accounting for leap years and maintaining consistency across various date scenarios.

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