Adventures in Machine Learning

Efficiently Converting Strings to Time Values in SQL Server

In SQL Server, the TIME data type is used to store time values. However, sometimes we may need to convert a string to a time value in SQL Server.

This conversion can be accomplished using various functions like PARSE(), CAST(), and CONVERT(). In this article, we will explore the steps involved in converting a string to a TIME value in SQL Server using these functions.

Converting a String to a TIME Value in SQL Server

Using PARSE() function

The PARSE() function in SQL Server is used to convert a string to a specified data type. When converting a string to a TIME value in SQL Server using the PARSE() function, we need to specify the format of the string.

Here’s an example:

PARSE(‘Monday 22:30:00’, ‘dddd HH:mm:ss’, ‘en-US’)

In this example, we are converting the string ‘Monday 22:30:00’ to a TIME value. ‘dddd HH:mm:ss’ is the format of the string, and ‘en-US’ specifies the language and culture to use.

The result of this function will be a TIME value representing 10:30:00 PM.

Using CAST() function

The CAST() function in SQL Server is used to convert an expression from one data type to another. When converting a string to a TIME value in SQL Server using the CAST() function, we need to specify the format of the string.

Here’s an example:

CAST(’22:30:00′ AS TIME)

In this example, we are converting the string ’22:30:00′ to a TIME value. Since the string is in a valid time format, we don’t need to specify the format.

Using CONVERT() function

The CONVERT() function in SQL Server is used to convert an expression from one data type to another. When converting a string to a TIME value in SQL Server using the CONVERT() function, we need to specify the format of the string.

Here’s an example:

CONVERT(TIME, ’22:30:00′, 108)

In this example, we are converting the string ’22:30:00′ to a TIME value. ‘108’ is the code for the time format ‘HH:mm:ss’.

Using the CASE() Function for Time Value without Additional Data

The CASE() function in SQL Server is used to evaluate a list of conditions and return a result. When using the CASE() function for time values without additional data, we can use a simple example where we set the conditions based on time intervals.

Here’s an example:

CASE

WHEN CONVERT(TIME, GETDATE()) BETWEEN ’06:00:00′ AND ’12:00:00′ THEN ‘Good morning!’

WHEN CONVERT(TIME, GETDATE()) BETWEEN ’12:00:00′ AND ’18:00:00′ THEN ‘Good afternoon!’

ELSE ‘Good evening!’

END

In this example, we are evaluating the current time using the GETDATE() function and returning a message based on the time interval. If the time is between 6:00 AM and 12:00 PM, the message will be ‘Good morning!’.

If the time is between 12:00 PM and 6:00 PM, the message will be ‘Good afternoon!’. Otherwise, the message will be ‘Good evening!’.

Conclusion

In this article, we explored the steps involved in converting a string to a TIME value in SQL Server using various functions like PARSE(), CAST(), and CONVERT(). We also explained how to use the CASE() function for time values without additional data.

By understanding these techniques, you can improve the efficiency of your SQL queries and retrieve the desired data with ease.

3) Adding Language Using the USING Keyword

The PARSE() function in SQL Server is commonly used for converting strings to various data types, including date and time values. One of the main advantages of PARSE() is its ability to handle a wide variety of input formats, including different languages and cultures.

To specify a language for the PARSE() function, the USING keyword can be used. The USING keyword must be followed by a culture code, which is used to specify the language and culture to use for the conversion.

The culture code must be a valid identifier that corresponds to a culture recognized by the .NET Framework. Here’s an example of using the USING keyword to specify a culture for the PARSE() function:

PARSE(‘lundi 19 avril 2021 14:35:45’, ‘dddd d MMMM yyyy HH:mm:ss’, ‘fr-FR’ USING ‘fr-FR’)

In this example, we’re converting a French date/time string to a date/time value using the PARSE() function.

The second argument in the PARSE() function specifies the format of the input string, while the third argument specifies the culture to use. The USING keyword is used to specify the culture code again for added clarity.

Note that if the USING keyword is not used to specify the culture, the default culture for the server will be used.

4) Performance of Conversion Functions

When working with large amounts of data in SQL Server, the performance of conversion functions like PARSE(), CAST(), and CONVERT() can play a crucial role in query execution time. While all three functions are designed to convert input data to the desired data type, the performance of each function can vary depending on several factors.

In general, the PARSE() and CONVERT() functions are more flexible than the CAST() function, as they support a wider range of input formats. However, this flexibility can come at the cost of performance, especially when converting large amounts of data.

The CAST() function is usually faster than the PARSE() and CONVERT() functions, as it does not require the same level of input format validation. However, the CAST() function may not be suitable for complex input formats that require more fine-tuned conversion rules.

To compare the performance of these functions, we can create a simple benchmark test using a large number of records. In this test, we’ll convert a string representation of a date/time value to a datetime2 data type using each of the three functions.

Here’s the benchmark test:

DECLARE @i INT = 1

DECLARE @count INT = 1000000

DECLARE @inputString VARCHAR(50) = ‘2021-04-19 14:35:45’

DECLARE @outputValue DATETIME2(7)

— CAST() function

SET STATISTICS TIME ON

WHILE @i <= @count

BEGIN

SET @outputValue = CAST(@inputString AS DATETIME2(7))

SET @i = @i + 1

END

SET STATISTICS TIME OFF

— CONVERT() function

SET STATISTICS TIME ON

SET @i = 1

WHILE @i <= @count

BEGIN

SET @outputValue = CONVERT(DATETIME2(7), @inputString, 120)

SET @i = @i + 1

END

SET STATISTICS TIME OFF

— PARSE() function

SET STATISTICS TIME ON

SET @i = 1

WHILE @i <= @count

BEGIN

SET @outputValue = PARSE(@inputString AS DATETIME2(7))

SET @i = @i + 1

END

SET STATISTICS TIME OFF

In this benchmark, we’re measuring the execution time of each function for a million iterations of the conversion process. The SET STATISTICS TIME ON and SET STATISTICS TIME OFF statements are used to enable and disable query execution time statistics, respectively.

Running this benchmark on a reasonably-sized SQL Server should show that the CAST() function is the fastest of the three conversion functions, followed by the CONVERT() function and then the PARSE() function. Overall, while performance considerations may be important when working with large amounts of data, it’s important to balance them with other factors like data format flexibility and ease of use.

The performance differences between these functions may not be significant enough for most applications, and using the function with the most appropriate syntax for a given scenario is often the best choice for developers. In conclusion, understanding how to convert a string to a time value in SQL Server using functions like PARSE(), CAST(), and CONVERT() is essential for efficiently retrieving data from a database.

Additionally, the USING keyword can be used with the PARSE() function to specify a language for the conversion. When it comes to performance, the CAST() function is usually faster than PARSE() and CONVERT().

Nonetheless, it’s essential to consider other factors like data format flexibility and ease of use when selecting a conversion function. Overall, this knowledge can help developers optimize SQL queries and improve the overall speed and accuracy of their applications.

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