Understanding the Format Datetime SQL Server Function

Welcome, Dev, to this comprehensive guide on the format datetime SQL Server function. In this article, we’ll take a deep dive into the function, its syntax and usage, and how to incorporate it into your database queries. Whether you’re a seasoned SQL Server user or just starting out, this guide will equip you with the tools and knowledge to master the format datetime function.

What is the Format Datetime SQL Server Function?

The format datetime function in SQL Server is used to convert a datetime data type to a formatted string. It allows you to customize the output format of the datetime value, such as displaying only the year, month, and day or adding separators between the date components. This function is particularly useful when you need to display datetime values in a specific format, such as for reporting or display purposes.

The syntax of the format datetime function is as follows:

Function Name	Parameters	Description
FORMAT	datetime_value, format_string	Converts a datetime value to a formatted string.

The datetime_value parameter is the datetime value you want to convert, while the format_string parameter specifies the output format of the string. The format_string parameter can include a combination of datetime format codes and separators, as we’ll discuss in more detail in the following sections.

Using the Format Datetime Function

To use the format datetime function, simply include it in your SQL query and specify the datetime value and format string parameters:

SELECT FORMAT(datetime_value, format_string) FROM table_name;

For example, to format a datetime value as “2021-12-01”, you can use the following query:

SELECT FORMAT('2021-12-01 13:45:30.1234567', 'yyyy-MM-dd') AS formatted_date;

This will return the formatted_date column with the value “2021-12-01”.

Using Date and Time Format Codes

The format datetime function supports a range of format codes that can be used to customize the output format of the datetime value. These codes are used to represent different parts of the date and time, such as year, month, day, hour, minute, and second. Here are some examples:

Format Code	Description
yyyy	Year as a four-digit number.
yy	Year as a two-digit number.
MM	Month as a two-digit number.
M	Month as a one or two-digit number.
dd	Day as a two-digit number.
d	Day as a one or two-digit number.
hh	Hour as a two-digit number (12-hour clock).
h	Hour as a one or two-digit number (12-hour clock).
HH	Hour as a two-digit number (24-hour clock).
H	Hour as a one or two-digit number (24-hour clock).
mm	Minute as a two-digit number.
m	Minute as a one or two-digit number.
ss	Second as a two-digit number.
s	Second as a one or two-digit number.

You can use these format codes to customize the output format of the datetime value in a variety of ways. For example, to display the date in the format “yyyy-MM-dd”, you can use the following format string:

'yyyy-MM-dd'

This will display the year, month, and day components of the datetime value separated by hyphens.

Using Date and Time Separators

In addition to using format codes, you can also include separators between the date and time components to further customize the output format of the datetime value. Common separators include hyphens, slashes, and colons. Here are some examples:

Separator	Description
–	Hyphen separator.
/	Slash separator.
:	Colon separator.
.	Period separator.

To include a separator in your format string, simply include it between the format codes. For example, to display the date in the format “yyyy/MM/dd”, you can use the following format string:

'yyyy/MM/dd'

This will display the year, month, and day components of the datetime value separated by slashes.

FAQ

What data types can the format datetime function convert?

The format datetime function can convert a datetime data type to a formatted string. It can also convert a date or time data type to a formatted string, as long as the input value can be implicitly converted to a datetime data type.

Can the format datetime function be used with other SQL functions?

Yes, the format datetime function can be used with other SQL functions to perform more complex operations on datetime values. For example, you can use the format datetime function to convert a datetime value to a string and then concatenate it with other strings using the SQL CONCAT function.

What happens if the format string is invalid?

If the format string is invalid, the format datetime function will return an error. It’s important to ensure that your format string is valid and follows the correct syntax before using it in your SQL queries.

Can you use the format datetime function to convert a string to a datetime value?

No, the format datetime function can only be used to convert a datetime value to a formatted string. To convert a string to a datetime value, you can use the SQL CONVERT or CAST functions.

What is the default date and time format in SQL Server?

The default date and time format in SQL Server is determined by the language and regional settings of the server. However, it’s generally recommended to use the format datetime function to specify a custom output format, as this ensures consistent formatting across different SQL Server environments.