Welcome, Dev, to this comprehensive guide on how to convert DateTime to Date in SQL Server. If you are a programmer or a database administrator dealing with SQL Server, you might find yourself needing to perform this conversion operation many times. This guide will help you understand the different methods and functions available to convert DateTime to Date efficiently. Let’s dive in!
Understanding the Basics of DateTime and Date
Before we delve into the conversion methods, let’s first understand the difference between DateTime and Date in SQL Server. DateTime is a data type that represents both date and time values. It consists of a date portion and a time portion, with the time portion measured in hours, minutes, and seconds. On the other hand, Date is a data type that represents only the date portion of a DateTime value, with the time portion set to 00:00:00. Understanding this basic difference is crucial for performing any DateTime to Date conversion.
DateTime Data Type
The DateTime data type is one of the most commonly used data types in SQL Server. It represents both the date and time values using eight bytes, where the first four bytes represent the number of days since January 1, 1900, and the last four bytes represent the number of milliseconds since midnight. You can create a DateTime value in different ways, such as:
Method |
Example |
|---|---|
Using the CAST() function |
SELECT CAST(‘2022-05-12 23:59:59.999’ AS DateTime) |
Using the CONVERT() function |
SELECT CONVERT(DateTime, ‘2022-05-12 23:59:59.999’) |
Using the GETDATE() function |
SELECT GETDATE() |
These methods create a DateTime value that consists of both the date and time portions.
Date Data Type
The Date data type, on the other hand, represents only the date portion of a DateTime value, with the time portion set to 00:00:00. It is a more precise representation of a date value without the time component. You can create a Date value in different ways, such as:
Method |
Example |
|---|---|
Using the CAST() function |
SELECT CAST(‘2022-05-12’ AS Date) |
Using the CONVERT() function |
SELECT CONVERT(Date, ‘2022-05-12’) |
Using the GETDATE() function |
SELECT CAST(GETDATE() AS Date) |
Note that the GETDATE() function returns both date and time values, and we need to use the CAST() function to convert it to a Date value.
Conversion Methods for DateTime to Date
Now that we have understood the basics of DateTime and Date, let’s explore the different conversion methods available in SQL Server. We will cover three primary methods:
- Using the CONVERT() function with style codes
- Using the CAST() function with DATEADD() function
- Using the DATE() function
Method 1: Using the CONVERT() Function with Style Codes
The CONVERT() function can be used to convert DateTime to Date by specifying the style code that represents the format of the DateTime value. The style codes determine the order and format of the date and time portions. Here’s an example:
DateTime Value |
Converted Date Value |
|---|---|
‘2022-05-12 23:59:59.999’ |
SELECT CONVERT(Date, ‘2022-05-12 23:59:59.999’, 120) |
The third parameter in the CONVERT() function represents the style code 120, which represents the format “yyyy-mm-dd hh:mi:ss”. It extracts only the date portion from the DateTime value and returns it as a Date value.
Here are some common style codes used to convert DateTime to Date:
Style Code |
Format |
|---|---|
101 |
mm/dd/yyyy |
102 |
yyyy.mm.dd |
110 |
yyyy-mm-dd |
120 |
yyyy-mm-dd hh:mi:ss |
Method 2: Using the CAST() Function with DATEADD() Function
The CAST() function can also be used to convert DateTime to Date by using the DATEADD() function. The DATEADD() function adds or subtracts a specified time interval to a DateTime value and returns a new DateTime value. Here’s an example:
DateTime Value |
Converted Date Value |
|---|---|
‘2022-05-12 23:59:59.999’ |
SELECT CAST(DATEADD(day, DATEDIFF(day, 0, ‘2022-05-12 23:59:59.999’), 0) AS Date) |
The DATEDIFF(day, 0, DateTimeValue) function calculates the number of days between the DateTime value and the base date ‘1900-01-01’, which is represented by the integer value 0. The DATEADD(day, …) function adds this number of days to the base date and returns a new DateTime value. Finally, we use the CAST() function to convert this DateTime value to a Date value.
Method 3: Using the DATE() Function
SQL Server 2008 introduced a new function called DATE() that can convert DateTime to Date. This function extracts only the date portion from a DateTime value and returns it as a Date value. Here’s an example:
DateTime Value |
Converted Date Value |
|---|---|
‘2022-05-12 23:59:59.999’ |
SELECT DATE(‘2022-05-12 23:59:59.999’) |
The DATE() function is the simplest and most efficient method to convert DateTime to Date in SQL Server 2008 or later versions. However, it might not be available in older versions of SQL Server.
Frequently Asked Questions
Q1. Why do we need to convert DateTime to Date?
A. There are many scenarios where we might need to perform this conversion, such as grouping data by date, filtering data by date, or calculating the number of days between two dates. By converting DateTime to Date, we can remove the time component and work with only the date component, which is more efficient and precise in many cases.
Q2. Can we convert a Date value to a DateTime value?
A. Yes, we can convert a Date value to a DateTime value by using the CAST() or CONVERT() function with a specific format. For example, SELECT CAST(‘2022-05-12’ AS DateTime) will return a DateTime value with the time portion set to 00:00:00.
Q3. How to handle null or invalid DateTime values?
A. When converting DateTime to Date, we need to handle null or invalid DateTime values to avoid errors. We can use the ISNULL() or COALESCE() function to replace null values with a default value, or use the TRY_CONVERT() or TRY_CAST() function to return a null value if the conversion fails.
Q4. Which conversion method is the fastest?
A. The DATE() function is the fastest conversion method as it is a built-in function in SQL Server and optimized for converting DateTime to Date. The CAST() function with DATEADD() function is the second fastest method, followed by the CONVERT() function with style codes. However, the performance difference is negligible in most cases, and we should choose the method based on the requirements and compatibility with the SQL Server version.
Q5. Can we convert a DateTime value to a Date value in other databases?
A. Yes, the conversion methods might differ, but most databases support the concept of DateTime and Date data types and provide functions or operators to convert between them. You should refer to the database documentation for the specific syntax and options.
Conclusion
Converting DateTime to Date is a common operation in SQL Server, and we have covered three main methods to perform this conversion. We have also understood the basics of DateTime and Date data types, their differences, and their usage. By following these methods, we can efficiently convert DateTime to Date and work with only the date component in our database queries and applications. We hope this guide has been helpful to you, Dev. Happy coding!