SQL Server Convert String to Datetime: A Comprehensive Guide for Dev

Hello Dev! Do you ever wonder how to convert a string into a datetime data type in SQL Server? If you are working on a project that involves date and time manipulation, this is a crucial task that you must know. In this article, we will guide you through the process of converting a string to a datetime data type in SQL Server. By the end of this article, you will be equipped with the knowledge to handle this task with ease. So, let’s dive in and explore this topic in detail.

Understanding Datetime Data Type

Datetime is a data type in SQL Server that is used to store date and time values. It is widely used in various applications that require date and time manipulation such as scheduling, tracking, and monitoring. In SQL Server, datetime has two subtypes: datetime and datetime2. The datetime subtype is accurate to a minute, while the datetime2 subtype is accurate to a nanosecond. These subtypes also differ in their storage size, with datetime2 having a larger storage size compared to datetime.

When we talk about converting a string to a datetime data type, we refer to the process of converting a string value that represents a date and time into a datetime data type. This process involves parsing the string value, checking its format, and converting it into a valid datetime value.

Converting String to Datetime in SQL Server

Converting a string to a datetime data type in SQL Server can be achieved using various methods. In this section, we will discuss the most commonly used methods for this task:

Method 1: Using CAST and CONVERT Functions

The CAST and CONVERT functions are built-in functions in SQL Server that are used to convert one data type into another. These functions can also be used to convert a string into a datetime data type.

To use CAST or CONVERT functions for converting a string to a datetime data type, you must specify the appropriate format for the input string. Here is an example:

DECLARE @date_string VARCHAR(25) = '2022-01-01 12:00:00 PM';DECLARE @datetime DATETIME = CAST(@date_string AS DATETIME);

In the above example, we declare a variable @date_string that contains a string value ‘2022-01-01 12:00:00 PM’. We then use the CAST function to convert this string into a datetime data type and store it in the @datetime variable. The result of this conversion is ‘2022-01-01 12:00:00 PM’, which is a valid datetime value.

Method 2: Using PARSE Function

The PARSE function is a built-in function in SQL Server 2012 and later versions that is used to parse a string value and convert it into a specified data type. This function can also be used to convert a string into a datetime data type.

The PARSE function requires two arguments: the input string and the format specifier. The format specifier is a string that specifies the format of the input string. Here is an example:

DECLARE @date_string VARCHAR(25) = '2022-01-01 12:00:00 PM';DECLARE @datetime DATETIME = PARSE(@date_string AS DATETIME USING 'en-US');

In the above example, we declare a variable @date_string that contains a string value ‘2022-01-01 12:00:00 PM’. We then use the PARSE function to convert this string into a datetime data type and store it in the @datetime variable. The second argument of the PARSE function specifies the format of the input string in ‘en-US’ culture. The result of this conversion is ‘2022-01-01 12:00:00 PM’, which is a valid datetime value.

Dealing with Invalid Date Formats

When converting a string into a datetime data type, it is important to ensure that the input string is in a valid format. Otherwise, the conversion may fail, and you may end up with an error. In this section, we will discuss some common invalid date formats and how to handle them.

Invalid Date Format 1: Ambiguous Date Format

Ambiguous date format refers to a date format that can be interpreted in multiple ways. For example, the date format ’01/02/2022′ can be interpreted as January 2, 2022 (MM/DD/YYYY) or February 1, 2022 (DD/MM/YYYY) depending on the culture. To handle this type of date format, you must ensure that the format specifier is unambiguous. Here is an example:

DECLARE @date_string VARCHAR(25) = '01/02/2022';DECLARE @datetime DATETIME = PARSE(@date_string AS DATETIME USING 'en-US');

In the above example, we declare a variable @date_string that contains a string value ’01/02/2022′. We then use the PARSE function to convert this string into a datetime data type and store it in the @datetime variable. The second argument of the PARSE function specifies the format of the input string as ‘en-US’ culture. This format specifier is unambiguous and ensures that the conversion is successful.

Invalid Date Format 2: Invalid Date Range

SQL Server has a range of valid date values from January 1, 1753, to December 31, 9999. If a string value falls outside this range, the conversion will fail, and you will get an error. To handle this type of date format, you must ensure that the input string falls within the valid date range. Here is an example:

DECLARE @date_string VARCHAR(25) = '1752-12-31';DECLARE @datetime DATETIME = PARSE(@date_string AS DATETIME USING 'en-US');

In the above example, we declare a variable @date_string that contains a string value ‘1752-12-31’. This value is outside the valid date range in SQL Server and will result in an error when we try to convert it into a datetime data type.

Frequently Asked Questions

What is the difference between CAST and CONVERT functions?

CAST and CONVERT functions are used to convert one data type into another data type in SQL Server. The difference between these functions is that CONVERT function allows you to specify a format for the output data type while the CAST function does not. If you want to convert a string to a datetime data type with a specific format, you should use the CONVERT function. Otherwise, you can use the CAST function.

How do I handle invalid date formats when converting a string to a datetime data type?

To handle invalid date formats, you must ensure that the input string is in a valid format and falls within the valid date range. If the input string is ambiguous, you must use an unambiguous format specifier. You can also handle invalid date formats by using a try-catch block to catch the conversion errors and handle them gracefully.

What is the difference between datetime and datetime2 subtypes in SQL Server?

Datetime and datetime2 are subtypes of the datetime data type in SQL Server. The difference between these subtypes is that datetime subtype is accurate to a minute, while the datetime2 subtype is accurate to a nanosecond. Datetime2 subtype also has a larger storage size compared to datetime.

Can I convert a string to a datetime data type using a user-defined format?

Yes, you can use a user-defined format to convert a string to a datetime data type in SQL Server. To do this, you can use the CONVERT function and specify your custom format in the format specifier argument. Here is an example:

DECLARE @date_string VARCHAR(25) = '01-Jan-2022 12:00:00 PM';DECLARE @datetime DATETIME = CONVERT(DATETIME, @date_string, 106);

In the above example, we convert a string value ’01-Jan-2022 12:00:00 PM’ to a datetime data type using the CONVERT function. The third argument of the CONVERT function specifies the format code 106, which corresponds to the format ‘dd mon yyyy hh:mi:ss:mmm AM’.

Conclusion

Converting a string to a datetime data type in SQL Server is a crucial task in date and time manipulation. In this article, we have discussed the methods for converting a string to a datetime data type using CAST, CONVERT and PARSE functions. We have also covered how to handle invalid date formats and some frequently asked questions related to this topic. By following the guidelines outlined in this article, you will be able to perform this task with ease and handle various scenarios that may arise during the conversion process.