How Can I Find the First Day of a Specific Week Number in MySQL?

Determining the First Day of a Week Using Week Number in MySQL

When dealing with date ranges, it often becomes necessary to determine the first day of a particular week. In MySQL, the WEEKNO function provides a convenient way to find the week number for a given date. However, to further refine our analysis, we may need to extract the first day of the week corresponding to a specific week number.

Consider a scenario where we have the week number 29 and we want to obtain the first day of that week. Using the WEEKNO function alone will not suffice. Instead, we can utilize the combination of DAYOFWEEK and ADDDATE functions to achieve this goal.

The DAYOFWEEK function determines the day of the week for a given date, with Sunday being represented by 1 and Saturday by 7. The ADDDATE function allows us to add or subtract a specified number of days from a date.

To derive the first day of a week given its week number, we can employ the following formula:

adddate(curdate(), INTERVAL 1-DAYOFWEEK(curdate()) DAY)

This expression adds (1 - DAYOFWEEK(curdate())) days to the current date. The curdate() function returns the current date, and DAYOFWEEK(curdate()) provides the current day of the week. By subtracting or adding days accordingly, we can arrive at the first day of the week based on the current day.

For instance, if we are currently in WEEK 29, and we want to know its first day, we can execute the following query:

select adddate(curdate(), INTERVAL 1-DAYOFWEEK(curdate()) DAY)

This query will return the first day of WEEK 29, which in our example would be Sunday, July 18th.

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