YEARWEEK() Function in MySQL

When working with dates in MySQL, the YEARWEEK() function is an essential tool for extracting the year and week numbers from a given date. This powerful function allows developers and data analysts to efficiently analyze and manipulate temporal data, enabling them to gain valuable insights and make informed decisions. In this comprehensive guide, we will dive deep into the YEARWEEK() function, exploring its syntax, parameters, and various use cases, along with practical examples and best practices.

Understanding the YEARWEEK() Function

 The MySQL YEARWEEK() function is a built-in date function that returns the year and week number for a given date. The returned value combines the year and week number into a single integer, making it convenient for storing and comparing date-related information. For example, if the input date is ‘2023-04-15’, the YEARWEEK() function would return the value 202315, indicating that the date belongs to the 15th week of the year 2023.

 This function is particularly useful when you need to perform data analysis based on weekly intervals spanning multiple years. By extracting the year and week number, you can easily group and aggregate data, identify trends, and generate meaningful reports.

Syntax of the YEARWEEK() Function

The syntax of the YEARWEEK() function is straightforward. It can be used in two forms:

1. YEARWEEK(date)
2. YEARWEEK(date, mode)

In the first form, the function takes a single parameter, date, which is the date from which the year and week number are to be extracted. The date parameter is required and must be a valid date or datetime expression.

In the second form, an additional mode parameter is included. This optional parameter influences how the week number is calculated. If the mode parameter is not specified, the function uses the value of the default_week_format system variable.

Return Value of the YEARWEEK() Function

The YEARWEEK() function returns a number that represents the year and week of the given date. The first four digits represent the year, and the last two digits represent the week number. For example, for the date ‘2023-12-29’, the function would return ‘202352’, indicating the 52nd week of 2023.

If the specified expression is not a valid date or datetime, or if the argument is NULL, the function returns NULL.

Understanding the Mode Parameter

The mode parameter in the YEARWEEK() function plays a crucial role in determining the week number. It affects the calculation of weeks in several ways, including the first day of the week, the minimum number of days in the first week, and the week number range.

The mode parameter can take values from 0 to 7, each corresponding to a different set of rules for calculating the week number. Here is a brief overview:

Basic Usage

To extract the year and week number from a specific date, you can simply pass the date value to the YEARWEEK() function:

SELECT YEARWEEK('2023-04-15');

This query will return the value 202315, indicating that the date ‘2023-04-15’ belongs to the 15th week of the year 2023.

Extracting Year and Week Separately

If you need to extract the year and week number separately, you can use the DIV and MOD functions in combination with YEARWEEK():

SELECT 
YEARWEEK('2023-04-15') DIV 100 AS year,
YEARWEEK('2023-04-15') MOD 100 AS week;

This query will return two columns: year with the value 2023 and week with the value 15.

Using Different mode Values

To illustrate how the mode parameter affects the result of the YEARWEEK() function, let’s consider a few examples:

SELECT 
YEARWEEK('2023-01-01', 0) AS mode_0,
YEARWEEK('2023-01-01', 1) AS mode_1,
YEARWEEK('2023-01-01', 2) AS mode_2,
YEARWEEK('2023-01-01', 3) AS mode_3;

This query will return the following result:

As you can see, the week number for ‘2023-01-01’ varies depending on the mode value used. With mode 0 and 1, the week number is 52 (belonging to the previous year), while with mode 2 and 3, the week number is 1 (belonging to the current year).

Getting Year and Week for the Current Date

To retrieve the year and week number for the current date, you can use the CURDATE() function in combination with YEARWEEK():

SELECT YEARWEEK(CURDATE());

This query will return the year and week number for the current date based on the default mode value.

Aggregating Data by Year and Week

The YEARWEEK() function is particularly useful when you want to aggregate data by year and week. For example, let’s say you have a table named sales with columns sale_date and amount. To calculate the total sales for each year and week, you can use the following query:

SELECT 
    YEARWEEK(sale_date) AS year_week,
    SUM(amount) AS total_sales
FROM 
    sales
GROUP BY 
    YEARWEEK(sale_date);

This query will group the sales data by the year and week number obtained from the sale_date column and calculate the total sales for each group.

Comparing Dates with YEARWEEK()

The YEARWEEK() function can be used in the WHERE clause of a query to find rows that match a specific year and week number. You can use comparison operators such as =, <, >, <=, >=, and <> to compare YEARWEEK() values.

For example, to find all rows in the sales table where the sale date belongs to the 15th week of 2023, you can use the following query:

SELECT *
FROM sales
WHERE YEARWEEK(sale_date) = 202315;

You can also find rows between a range of year and week values using the BETWEEN operator:

SELECT *
FROM sales
WHERE YEARWEEK(sale_date) BETWEEN 202301 AND 202312;

This query will retrieve all rows where the sale date falls within the first 12 weeks of 2023.

When using YEARWEEK() in comparison operations, it’s important to consider the performance implications. If the column being compared is not indexed, the query may perform a full table scan, which can be slow for large tables. In such cases, it’s recommended to create an index on the relevant column to improve query performance.

Formatting YEARWEEK() Results

Sometimes, you may need to format the result of the YEARWEEK() function to extract the year and week number into separate columns or to display the week number in a specific format.

Extracting Year and Week into Separate Columns

To extract the year and week number into separate columns, you can use the DIV and MOD functions as mentioned earlier:

SELECT
    YEARWEEK(sale_date) DIV 100 AS year,
    YEARWEEK(sale_date) MOD 100 AS week,
    amount
FROM
    sales;

This query will return the year, week number, and amount for each row in the sales table.

Padding Week Number with Leading Zeros

If you want to display the week number with leading zeros (e.g., ’01’ instead of ‘1’), you can use the LPAD() function:

SELECT
    YEARWEEK(sale_date) DIV 100 AS year,
    LPAD(YEARWEEK(sale_date) MOD 100, 2, '0') AS week,
    amount
FROM
    sales;

The LPAD() function pads the week number with leading zeros to ensure a consistent two-digit format.

Displaying Week Number Ranges

In some cases, you may want to display the week number range instead of individual week numbers. You can achieve this by concatenating the start and end week numbers:

SELECT
    CONCAT('Weeks ', MIN(YEARWEEK(sale_date) MOD 100), '-', MAX(YEARWEEK(sale_date) MOD 100)) AS week_range,
    SUM(amount) AS total_sales
FROM
    sales
GROUP BY
    YEARWEEK(sale_date) DIV 100;

This query groups the sales data by year and displays the week range (e.g., ‘Weeks 1-12’) along with the total sales for each year.

Converting Year and Week Back to a Date

If you have the year and week number and want to convert it back to a date, you can use the STR_TO_DATE() function:

SELECT STR_TO_DATE(CONCAT(year, week, ' Monday'), '%X%V %W') AS date
FROM
    (SELECT 2023 AS year, 15 AS week) AS subquery;

Conclusion

The MySQL YEARWEEK() function is a powerful tool for extracting the year and week number from a given date. By understanding its syntax, parameters, and various use cases, you can effectively analyze and manipulate temporal data in your MySQL database.

Throughout this comprehensive guide, we explored the different aspects of the YEARWEEK() function, including its behavior with different mode values, practical examples, formatting techniques, troubleshooting tips, and best practices.

By mastering the YEARWEEK() function, you can unlock valuable insights from your date-based data and make informed decisions in your applications. Whether you are a developer working on data analysis tasks or a data analyst exploring trends and patterns, the YEARWEEK() function is an essential tool in your MySQL toolkit.

Remember to consider the specific requirements of your application, optimize query performance, and ensure portability when using the YEARWEEK() function. With practice and experimentation, you’ll be able to leverage the full potential of this versatile function and take your date-based analysis to the next level.