Finding the first day of a week based on a given date can sometimes be a complex task.
However, with the introduction of the DATEPART function in SQL Server 2022, this process has become much simpler.
In this blog post, we will explore how to use this function to find the first day of a week based on a given date. We will also discuss how the output can vary depending on the DATEFIRST setting in your SQL Server.
Let's take the example of today's date as a timestamp value.
We will use the DATEPART function to define the week as the date part that we want to obtain from the given date.
Here is an example query: \`\`\` SELECT DATEPART(WEEK, GETDATE()) AS FirstDayOfWeek \`\`\`
When we execute this query, the output will be the first day of the current week.
For example, if today's date is January 21, 2024, the output will be "January 21, 2024" which is the date for the starting Sunday of this week.
It is important to note that the output of this query can vary depending on the date first setting in your SQL Server.
The date first setting defines which day of the week you have defined as the first day for that week.
Therefore, if you have set Monday as the first day of the week in your SQL Server, the output will be the first Monday of the week instead of Sunday.
Other Date Parts
The DATEPART function can also be used to calculate values of other date parts like year, month, etc.
For example, if we want to find the year of a given date, we can modify the query as follows:
\`\`\` SELECT DATEPART(YEAR, GETDATE()) AS Year \`\`\`
Similarly, if we want to find the month of a given date, we can modify the query as follows:
\`\`\` SELECT DATEPART(MONTH, GETDATE()) AS Month \`\`\`
This flexibility of the DATEPART function allows us to easily extract specific date parts from a given date.
Another interesting use case of the DATEPART function is to calculate the first day of a quarter for a specific date.
To achieve this, we can modify the query as follows:
\`\`\` SELECT DATEFROMPARTS(DATEPART(YEAR, GETDATE()), ((DATEPART(QUARTER, GETDATE()) - 1) \* 3) + 1, 1) AS FirstDayOfQuarter \`\`\`
In this query, we use the DATEFROMPARTS function to construct a new date using the year, quarter, and day values.
We calculate the quarter value by subtracting 1 from the result of the DATEPART function for the quarter of the given date.
We then multiply this value by 3 and add 1 to get the month value for the first month of the quarter.
Finally, we set the day value to 1 to get the first day of the quarter.
By using this technique, we can easily find the first day of a quarter for any given date.
Whether you're a SQL Server developer or a data analyst, mastering the DATEPART function can greatly simplify your date calculations and enhance your productivity. So go ahead, give it a try, and make your date calculations more efficient than ever before.