Summary: in this tutorial, you will learn how to use the MySQL WEEK function to get the week number for a date.

Introduction to MySQL WEEK function

Typically, a year has 365 days for a normal year and 366 days for leap year. A year is then divided into weeks with each week has exact 7 days. So for a year we often has 365 / 7 = 52 weeks that range from 1 to 52.

To check whether a particular date belongs to which week number, you use the WEEK function as follows:

Code language: SQL (Structured Query Language) (sql)

The WEEK function accepts two arguments:

• date is the date that you want to get a week number.
• mode is an optional argument that determines the logic of week number calculation. It allows you to specify whether the week should start on Monday or Sunday and the returned week number should be between 0 and 52 or 0 and 53.

If you ignore the mode argument, the WEEK function will use the value of the default_week_format system variable by default.

To get the current value of default_week_format variable, you use the SHOW VARIABLES statement as follows:

Code language: SQL (Structured Query Language) (sql)

In our server, the default value of  default_week_format is 0. The following table illustrates how the mode argument influcences the WEEK function:

The ” with 4 or more days this year” in the above table means:

• If the week that contains January 1st and has 4 or more days in the new year, the week is numbered as week 1.
• Otherwise, the week is numbered as the last week of the previous year and the next week is week 1.

The WEEK function returns a week number followed according to ISO 8601:1988

MySQL WEEK function example

See the following orders table in the sample database.

The following statement returns the number of orders per week in 2013 using the WEEK function:

Code language: SQL (Structured Query Language) (sql)

In this tutorial, you have learned how to use the MySQL WEEK function to get the week number from a specified date.