How to Efficiently Remove the Time Component from a DateTime Value in SQL Server?

Optimizing Datetime Data: Removing the Time Component in SQL Server

The Challenge:

Working with datetime fields often requires isolating the date portion, excluding the time. This article explores the most efficient method for this common SQL Server task.

Recommended Approach:

After comparing different techniques, the most efficient and flexible solution is:

<code class="language-sql">SELECT DATEADD(dd, DATEDIFF(dd, 0, GETDATE()), 0)</code>

Performance Analysis:

This method consistently demonstrates superior performance, especially with large datasets. Its inherent flexibility extends to calculating other date-related values (e.g., determining the first day of the month).

Alternative Methods and Limitations:

Converting to varchar using CONVERT(char(11), GETDATE(), 113) offers acceptable performance in some cases, but carries potential risks. Language/date format inconsistencies can arise due to the varchar conversion. Furthermore, this method lacks the adaptability of the DATEADD/DATEDIFF approach.

SQL Server 2008 and Beyond:

SQL Server 2008 and later versions provide a streamlined alternative: direct casting to date. For example: CAST(GETDATE() AS DATE). This simplifies the process significantly.

Indexing and Performance Considerations:

Using functions or CAST operations within WHERE clauses can negatively impact index utilization. Careful planning is essential to maintain optimal query performance.

Handling datetime2:

The same principles apply to datetime2 (introduced in SQL Server 2008 and enhanced in SQL Server 2019). Here's an example:

<code class="language-sql">DECLARE @datetime2value datetime2 = '02180912 11:45'; -- Year 0218 for demonstration within datetime2 range
DECLARE @datetime2epoch datetime2 = '19000101';

SELECT DATEADD(dd, DATEDIFF(dd, @datetime2epoch, @datetime2value), @datetime2epoch);</code>

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