How SQL Server Converts DateTime to Date: A Comprehensive Guide for Devs

Hello Devs! Welcome to our guide on how SQL Server converts DateTime to Date. In this article, we will take a deep dive into the world of SQL Server and discuss everything you need to know about this conversion process. Whether you are a beginner or an experienced developer, this article is for you. So, let’s get started!

What is DateTime in SQL Server?

Before we dive into the conversion process, let’s first understand what DateTime is in SQL Server. DateTime is a data type in SQL Server that represents a date and time value. The date and time values are stored in a single field and can be manipulated using various built-in functions.

A DateTime value is represented in the following format: YYYY-MM-DD HH:MI:SS, where:

• YYYY: Year (four digits)
• MM: Month (two digits)
• DD: Day (two digits)
• HH: Hour (two digits, 24-hour format)
• MI: Minute (two digits)
• SS: Second (two digits)

Now that we have a basic understanding of DateTime, let’s move on to the conversion process.

Converting DateTime to Date in SQL Server

Converting DateTime to Date in SQL Server can be done using various built-in functions. Here are some of the most commonly used functions:

1. CONVERT Function

The CONVERT function converts a value from one data type to another. To convert DateTime to Date using CONVERT, you can use the following syntax:

Syntax:	CONVERT(date, datetime_column)
Description:	Converts a DateTime value to a Date value

For example, let’s say we have a table named “orders” with a DateTime column named “order_date”. To convert the “order_date” column to a Date column, we can use the following SQL statement:

SELECT CONVERT(date, order_date) AS order_date FROM orders

This will return a new column named “order_date” with only the date values.

2. CAST Function

The CAST function converts an expression of one data type to another. To convert DateTime to Date using CAST, you can use the following syntax:

Syntax:	CAST(datetime_column AS date)
Description:	Converts a DateTime value to a Date value

For example, let’s say we have the same “orders” table with a DateTime column named “order_date”. To convert the “order_date” column to a Date column, we can use the following SQL statement:

SELECT CAST(order_date AS date) AS order_date FROM orders

This will return a new column named “order_date” with only the date values.

3. DATE Function

The DATE function returns the date part of a DateTime value. To use the DATE function, you can use the following syntax:

Syntax:	DATE(datetime_column)
Description:	Returns the date part of a DateTime value

For example, let’s say we have the same “orders” table with a DateTime column named “order_date”. To extract the date values from the “order_date” column, we can use the following SQL statement:

SELECT DATE(order_date) AS order_date FROM orders

This will return a new column named “order_date” with only the date values.

4. DATEADD Function

The DATEADD function adds or subtracts a specified time interval from a DateTime value. To use the DATEADD function to extract the date part of a DateTime value, you can use the following syntax:

Syntax:	DATEADD(day, DATEDIFF(day, 0, datetime_column), 0)
Description:	Returns the date part of a DateTime value

For example, let’s say we have the same “orders” table with a DateTime column named “order_date”. To extract the date values from the “order_date” column, we can use the following SQL statement:

SELECT DATEADD(day, DATEDIFF(day, 0, order_date), 0) AS order_date FROM orders

This will return a new column named “order_date” with only the date values.

5. LEFT Function

The LEFT function returns a specified number of characters from the start of a string. To use the LEFT function to extract the date part of a DateTime value, you can use the following syntax:

Syntax:	LEFT(CONVERT(varchar, datetime_column, 120), 10)
Description:	Returns the first 10 characters of a DateTime value

For example, let’s say we have the same “orders” table with a DateTime column named “order_date”. To extract the date values from the “order_date” column, we can use the following SQL statement:

SELECT LEFT(CONVERT(varchar, order_date, 120), 10) AS order_date FROM orders

This will return a new column named “order_date” with only the date values.

FAQ

1. Why do I need to convert DateTime to Date?

There are many reasons why you may need to convert DateTime to Date. For example, you may want to extract only the date values from a DateTime column for reporting purposes, or you may want to join two tables on their date values.

2. Can I convert Date to DateTime?

Yes, you can convert Date to DateTime using various built-in functions such as CONVERT and CAST. The process is similar to converting DateTime to Date.

3. Are there any limitations to converting DateTime to Date?

One limitation is that when you convert DateTime to Date, you lose the time part of the value. This may not be an issue in some cases, but it can be problematic if you need the time values for certain operations. In addition, depending on the conversion function used, there may be a performance impact.

4. Which conversion function should I use?

It depends on your specific use case and personal preference. All of the conversion functions discussed in this article will give you the same result, so it’s up to you to decide which one to use.

5. Are there any best practices for converting DateTime to Date?

One best practice is to ensure that you use the appropriate data types for your columns. If you only need the date values, it’s better to store them in a Date column rather than a DateTime column. In addition, be mindful of any performance implications when converting data types.

That’s it for our guide on how SQL Server converts DateTime to Date. We hope you found it useful and informative. If you have any questions or comments, please feel free to leave them below. Happy coding!