Determining weekday from date in MS SQL Server

Data and Databases
1

Hey everyone,

I’m working on a project where I need to figure out the day of the week for a specific date in Microsoft SQL Server. For example, if I have the date 03/15/2023, I want to know if it’s a Monday, Tuesday, or whatever.

I’m not sure if there’s a built-in function for this in SQL Server or if I need to create some kind of lookup table. Has anyone done this before? What’s the easiest way to get this info?

I’d really appreciate any tips or code snippets you could share. Thanks in advance for your help!

-- Example of what I'm trying to do
DECLARE @SampleDate DATE = '2023-03-15';
-- How can I get the weekday name from this date?

Let me know if you need any more details about what I’m trying to accomplish.

2

In SQL Server, you can efficiently determine the weekday from a date using the DATENAME function, as mentioned earlier. However, if you need to perform this operation frequently or on large datasets, consider creating a calendar table. This approach can significantly improve query performance.

A calendar table is a pre-populated table containing date-related information, including weekdays. You can join this table with your main dataset to quickly retrieve weekday information without repeatedly calculating it.

Here’s a basic example of how to create and use a calendar table:

CREATE TABLE Calendar (
    Date DATE PRIMARY KEY,
    DayOfWeek VARCHAR(10)
);

-- Populate the table (you'd typically do this for several years)
INSERT INTO Calendar (Date, DayOfWeek)
SELECT TOP (366) 
    DATEADD(DAY, ROW_NUMBER() OVER (ORDER BY a.object_id) - 1, '2023-01-01') AS Date,
    DATENAME(WEEKDAY, DATEADD(DAY, ROW_NUMBER() OVER (ORDER BY a.object_id) - 1, '2023-01-01')) AS DayOfWeek
FROM sys.all_objects a
CROSS JOIN sys.all_objects b;

-- Usage
SELECT c.DayOfWeek
FROM YourTable y
JOIN Calendar c ON y.SomeDate = c.Date;

This method can be particularly beneficial for complex queries or large datasets.

3

oh cool question! i’ve always wondered about date stuff in sql. have you tried any solutions yet? what kinda project are you working on that needs weekdays? sounds interesting! maybe we could brainstorm some creative ways to use this data in your app?

4

hey swimmingfish, u can use the DATENAME function for this. it’s super easy:

SELECT DATENAME(WEEKDAY, @SampleDate) AS WeekdayName

this’ll give u the full weekday name. if u want just the number, use DATEPART instead. hope this helps!