How Can I Efficiently Extract the Date Component from a DateTime Value in SQL Server?

Get the date component of Datetime value in SQL Server

Extracting date components from Datetime values ​​is a common task in SQL Server. An efficient method is to use the DATEADD function.

Use the DATEADD function:

<code class="language-sql">SELECT DATEADD(DAY, DATEDIFF(DAY, 0, CRETS), 0) FROM tblMeasureLogv2</code>

Here, CRETS are datetime columns. By using DATEADD, we specify the number of dates to add to the datetime value, in this case zero. This essentially resets the hour, minute, and second components of the value to midnight, resulting in the date portion.

Comparison with other methods:

The DATEADD method executes slightly faster than the floor-float conversion method proposed by Matt. Other commonly used methods, such as STRINGCONVERT and pure SELECT statements, are significantly slower in comparison.

Performance evaluation:

In testing on a very large table containing over 130 million rows, the DATEADD method demonstrated the following performance:

<code>SQL Server 执行时间：CPU时间 = 531 毫秒，经过时间 = 33440 毫秒</code>

In comparison, the CPU time for the floor-cast method is 625 milliseconds, and the CPU time for the string conversion method is 1953 milliseconds. This shows that the DATEADD method is more efficient in this particular test environment.

Conclusion:

In SQL Server, using the DATEADD function provides an efficient way to truncate a datetime value into its date component. Its simplicity and speed make it a suitable choice for a variety of data processing scenarios.

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