How to Find the First Day of a Week Given Its Week Number in MySQL?

Determining the First Day of the Week from Week Number in MySQL

A common task in data analysis or calendar management is determining the first day of a week based on its week number. In MySQL, we can leverage a simple technique to extract this information.

Solution:

To retrieve the first day of a particular week from its week number, we can utilize the following query:

SELECT DATE(DATE_SUB(DATE(DATE_ADD(NOW(), INTERVAL 1 DAY)), INTERVAL WEEKDAY(DATE(DATE_ADD(NOW(), INTERVAL 1 DAY))) + 1 DAY)) AS WeekStart;

Explanation:

• DATE_ADD(NOW(), INTERVAL 1 DAY): This adds one day to the current date and converts it to a DATE value, ensuring we start with Monday-based week numbering.
• WEEKDAY(): This function returns the weekday number (0 for Sunday, 6 for Saturday) of the given date.
• DATE_SUB(): We subtract the weekday number plus 1 from the date to retrieve the Sunday (first day of the week). The addition of 1 is necessary because WEEKDAY() returns 0 for Sunday, while Sunday should be shifted to the end of the week numbering scheme.
• DATE(): Finally, we apply the DATE() function to remove the time component and return only the date.

Example:

Let's calculate the first day of the current week, which is week 29:

SELECT DATE(DATE_SUB(DATE(DATE_ADD(NOW(), INTERVAL 1 DAY)), INTERVAL WEEKDAY(DATE(DATE_ADD(NOW(), INTERVAL 1 DAY))) + 1 DAY)) AS WeekStart;

This query will return the date "2023-07-18", which corresponds to Sunday, the first day of week 29.

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