How to Convert Date in SQL Server: A Comprehensive Guide for Dev

Greetings Dev! As a developer, you understand the importance of manipulating data in SQL Server. One of the most common tasks is converting date values. Dates are an important part of any database application and may need to be formatted, transformed or manipulated to suit specific business requirements. In this article, we will explore the different methods of converting date formats in SQL Server. From basic data types to more complex date functions, this guide will provide you with all the necessary tools for successful data manipulation.

Understanding Date Formats

Before we dive into date conversion, it is essential to understand the different date formats used in SQL Server. SQL Server stores dates using the DATETIME data type, which includes both the date and time values. The date format used by SQL Server is YYYY-MM-DD HH:MI:SS. However, the format can be customized by using different functions and styles.

The Date and Time Data Types in SQL Server

SQL Server has several data types for storing date and time values. Below are the most commonly used ones:

Data Type	Definition
DATE	Stores only date values in YYYY-MM-DD format
TIME	Stores only time values in HH:MI:SS format
DATETIME	Stores both date and time values in YYYY-MM-DD HH:MI:SS format
SMALLDATETIME	Stores both date and time values in YYYY-MM-DD HH:MI format

The datetime2 Data Type

SQL Server 2008 introduced a new data type called datetime2 that has a precision of up to 7 decimal places, compared to the 3 decimal places supported by the DATETIME data type. This means that datetime2 supports a wider range of date and time values, from January 1, 0001, to December 31, 9999. It also allows you to specify the precision of the time portion, ranging from 0 to 7 decimal places.

Methods for Converting Date Formats

Converting a Date to a String with the CONVERT Function

The CONVERT function is used to convert a date or time value to a string value. It takes three parameters: the target data type, the source value, and an optional style argument. The style argument specifies the format of the string value, and it can be used to customize the output of the CONVERT function.

Here’s an example of how to use the CONVERT function to format a date value as a string:

SELECT CONVERT(VARCHAR(10), GETDATE(), 111) AS [Date String] 

This will return the current date in YYYY/MM/DD format.

Converting a String to a Date with the CONVERT Function

In addition to converting a date to a string, the CONVERT function can also be used to convert a string to a date. The syntax is similar to the previous example, except that the parameters are reversed.

Here’s an example:

SELECT CONVERT(DATETIME, '2022-04-20', 126) AS [Date Value] 

This will convert the string ‘2022-04-20’ to a DATETIME value, using the ISO 8601 format.

Converting a Date to a String with the FORMAT Function

The FORMAT function was introduced in SQL Server 2012 and is used to format a date or time value as a string. It takes two parameters: the target format string and the source value. The target format string specifies the desired output format, and it can be customized to include different date and time elements.

Here’s an example of how to use the FORMAT function to format a date value as a string:

SELECT FORMAT(GETDATE(), 'yyyy/MM/dd') AS [Date String] 

This will return the current date in YYYY/MM/DD format.

Converting a String to a Date with the PARSE Function

The PARSE function was also introduced in SQL Server 2012 and is used to convert a string to a date or time value. It takes two parameters: the source value and the target data type. The target data type specifies the desired output data type, and it can be any of the date or time data types supported by SQL Server.

Here’s an example of how to use the PARSE function to convert a string to a datetime value:

SELECT PARSE('2022-04-20 15:30', 'yyyy-MM-dd HH:mm') AS [Date Value] 

This will convert the string ‘2022-04-20 15:30’ to a DATETIME value, using the custom format string ‘yyyy-MM-dd HH:mm’.

FAQ

1. What is the default date format in SQL Server?

The default date format in SQL Server is YYYY-MM-DD HH:MI:SS.

2. How do I format a date in SQL Server?

You can format a date in SQL Server using the CONVERT or FORMAT functions.

3. How can I convert a string to a date in SQL Server?

You can use the CONVERT or PARSE function to convert a string to a date in SQL Server.

4. What is the difference between DATETIME and datetime2 data types?

The main difference between DATETIME and datetime2 data types is the level of precision. datetime2 supports up to 7 decimal places, while DATETIME supports only 3.

5. Can I customize the output format of the CONVERT and FORMAT functions?

Yes, you can customize the output format of the CONVERT and FORMAT functions by using the appropriate style or format string.

Conclusion

In conclusion, manipulating dates in SQL Server is an essential task for developers. Whether you need to convert a date to a string or vice versa, understanding the different data types and conversion methods is critical for successful data manipulation. By using the techniques and functions discussed in this article, you can easily convert date formats in SQL Server to meet your specific business requirements.