MySQL WEEKDAY Function

The WEEKDAY function in MySQL is a powerful tool for anyone working with database management and date manipulations. This function helps you determine the day of the week for a specific date, simplifying the process of scheduling, querying, and programming logic related to dates. Whether you’re building applications that require date calculations or simply looking for a way to sort data by day, understanding the WEEKDAY function is essential.

1. Introduction

The WEEKDAY function is a date function in MySQL that returns the index (0-6) representing the day of the week for a given date. The function is particularly useful in scenarios where you need to check for specific days, filter records based on the day, or perform calculations tied to weekly schedules.

2. Syntax

The syntax of the WEEKDAY function is straightforward:

WEEKDAY(date)

In this syntax:

• date: This parameter represents the date value you want to evaluate. It can be a date column in your database or any valid date formatted as ‘YYYY-MM-DD’.

3. Return Values

The WEEKDAY function returns an integer value:

• 0: Represents Monday
• 1: Represents Tuesday
• 2: Represents Wednesday
• 3: Represents Thursday
• 4: Represents Friday
• 5: Represents Saturday
• 6: Represents Sunday

This mapping allows developers to easily perform operations based on the day of the week and can be particularly useful when combined with other date functions.

4. Examples

Let’s explore some practical examples to better understand how to use the WEEKDAY function in MySQL.

Basic Usage Example

This example shows how to utilize the WEEKDAY function to find out what day of the week is September 22, 2023.

SELECT WEEKDAY('2023-09-22') AS DayIndex;

The query returns:

DayIndex
4

This result indicates that September 22, 2023, is a Friday since it corresponds to the index 4.

Using WEEKDAY in a Table

Suppose we have a table named events that contains a column event_date.

CREATE TABLE events (
    id INT AUTO_INCREMENT PRIMARY KEY,
    event_name VARCHAR(255),
    event_date DATE
);

INSERT INTO events (event_name, event_date) VALUES 
('New Year', '2023-01-01'),
('Labor Day', '2023-05-01'),
('Independence Day', '2023-07-04'),
('Thanksgiving', '2023-11-24');

We can retrieve the day of the week for each event using the following SQL query:

SELECT event_name, event_date, WEEKDAY(event_date) AS DayIndex 
FROM events;

The result would be:

Event Name	Event Date	DayIndex
New Year	2023-01-01	6
Labor Day	2023-05-01	0
Independence Day	2023-07-04	2
Thanksgiving	2023-11-24	5

Filtering Records by Day

You can also use the WEEKDAY function to create conditional queries. For instance, if you want to find all events that occur on a weekend (Saturday and Sunday), you can use:

SELECT event_name, event_date 
FROM events 
WHERE WEEKDAY(event_date) IN (5, 6);

This would return:

Event Name	Event Date
New Year	2023-01-01

Combining with Other Functions

The WEEKDAY function can be used alongside other MySQL date functions for advanced calculations. Here is an example where we find the day of the week for the first day of the month:

SELECT MONTH(event_date) AS month, WEEKDAY(event_date) AS DayIndex
FROM events 
WHERE DAY(event_date) = 1;

Result:

Month	DayIndex
1	6

5. Related Functions

MySQL offers a variety of other date functions that work well with WEEKDAY:

Function	Description
DAYOFWEEK()	Returns the index (1-7) of the day of the week for the date, with Sunday as 1.
DATE_FORMAT()	Formats a date as per the specified format, helpful for outputting the day name.
WEEK()	Returns the week number for the given date.
DAY()	Returns the day of the month for a given date.

6. Conclusion

The WEEKDAY function is a vital tool for date manipulation in MySQL. Understanding how to efficiently use this function can greatly enhance your ability to manage and analyze date data in your applications. Always consider exploring other date functions that complement the WEEKDAY function to fully realize the potential of date operations in MySQL.

FAQ

Q1: What if I provide an invalid date to the WEEKDAY function?

A1: The WEEKDAY function will return NULL if the provided date is invalid.

Q2: Can the WEEKDAY function work with datetime values?

A2: Yes, the WEEKDAY function can accept both DATE and DATETIME values; it will ignore the time part.

Q3: How does WEEKDAY differ from DAYOFWEEK?

A3: WEEKDAY returns 0 for Monday and 6 for Sunday, while DAYOFWEEK returns 1 for Sunday and 7 for Saturday.

Q4: Can I use WEEKDAY in a WHERE clause?

A4: Yes, you can use WEEKDAY as part of a WHERE clause to filter records based on the day of the week.

Q5: Is the WEEKDAY function affected by timezone settings?

A5: The WEEKDAY function returns the day based on the date provided. However, make sure that your date values respect your database’s timezone settings to avoid discrepancies.