Convert to Datetime in SQL Server

Welcome, Dev, to this informative article about converting to datetime in SQL Server. Date and time is an essential aspect of data analysis, and SQL Server provides powerful tools to manage date and time values. In this article, we will explore the different techniques to convert date and time data types in SQL Server.

Understanding Datetime Data Types

In SQL Server, datetime data types are used to represent dates and times. The most commonly used datatypes for this purpose are:

Datatype	Description
DATE	Stores only the date portion in yyyy-mm-dd format
TIME	Stores only the time portion in hh:mm:ss format
DATETIME	Stores both date and time in yyyy-mm-dd hh:mm:ss format

Now, let’s dive into the techniques to convert to datetime in SQL Server.

Using CAST Function

The CAST function can be used to convert a value of one data type to another. To convert a value to datetime, we can use the following syntax:

SELECT CAST('2019-06-15' AS datetime);

This will return the datetime value ‘2019-06-15 00:00:00.000’.

Similarly, to convert a value to date or time, we can use:

SELECT CAST('12:30:45' AS time);

This will return the time value ’12:30:45.0000000′.

Limitations of CAST Function

The CAST function is limited in its ability to handle different date and time formats. If the format of the input value is not recognized by the CAST function, it will return an error. In such cases, we can use the CONVERT function instead.

Using CONVERT Function

The CONVERT function is used to convert a value of one data type to another, just like the CAST function. However, it provides more flexibility in handling different date and time formats.

The general syntax of the CONVERT function is:

SELECT CONVERT(target_data_type, source_value, [optional_format]);

Here, the target_data_type is the data type to which we want to convert the value, the source_value is the input value, and the optional_format is the format of the input value, in case it is not recognized by the CONVERT function.

Converting to Datetime

To convert a value to datetime using CONVERT, we can use the following syntax:

SELECT CONVERT(datetime, '2019-06-15');

This will return the datetime value ‘2019-06-15 00:00:00.000’.

Converting to Date or Time

To convert a value to date or time using CONVERT, we can use:

SELECT CONVERT(date, '2019-06-15');

This will return the date value ‘2019-06-15’.

SELECT CONVERT(time, '12:30:45');

This will return the time value ’12:30:45.0000000′.

Using Optional Format

In case the input value is not recognized by the CONVERT function, we can use the optional_format parameter to specify the format explicitly.

SELECT CONVERT(datetime, '15-06-2019', 105);

This will return the datetime value ‘2019-06-15 00:00:00.000’.

Table of Format Codes

The following format codes can be used with the optional_format parameter to handle different date and time formats:

Code	Description
101	mm/dd/yyyy
102	yyyy.mm.dd
103	dd/mm/yyyy
105	dd-mm-yyyy
108	hh:mm:ss

Frequently Asked Questions

What is the difference between DATE and DATETIME data types?

The DATE data type stores only the date portion in the format yyyy-mm-dd, while the DATETIME data type stores both date and time in the format yyyy-mm-dd hh:mm:ss.

Can we convert a string to datetime without specifying the format?

Yes, if the input string is in a recognized format, both CAST and CONVERT functions can convert it to datetime without specifying the format. However, if the format is not recognized, we need to specify it explicitly using the optional_format parameter.

Can we convert a datetime value to a different time zone?

Yes, SQL Server provides functions like AT TIME ZONE and SWITCHOFFSET to convert datetime values to a different time zone. However, this is beyond the scope of this article.

Conclusion

In this article, we have explored the different techniques to convert to datetime data types in SQL Server. We have seen how to use the CAST and CONVERT functions, and how the optional_format parameter can be used to handle different date and time formats. We hope this article has been informative and helpful.