How to Efficiently Remove the Time Portion from a SQL Server Datetime Field?

Optimizing Date Extraction from SQL Server datetime Fields

Extracting just the date portion from a SQL Server datetime field is a common task. Two prevalent approaches are compared here for efficiency:

Method A:

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

Method B:

<code class="language-sql">SELECT CAST(CONVERT(CHAR(11), GETDATE(), 113) AS DATETIME)</code>

Performance Benchmark

While both methods are generally fast, Method A consistently demonstrates superior performance, particularly with larger datasets. Testing on a million-row dataset revealed significantly lower CPU consumption using Method A, highlighting its efficiency.

Additional Factors

Beyond speed, other considerations influence method selection:

• Locale and Date Formatting: Method B's reliance on CONVERT to CHAR introduces potential issues with locale-specific date formats.
• Data Type Handling: Method B utilizes FLOAT internally, which may have storage implications.
• Extensibility: Method A provides greater flexibility for extending calculations (e.g., finding the first day of the month or the next day).

SQL Server 2008 and Later

For SQL Server 2008 and subsequent versions, the CAST function offers a streamlined alternative:

<code class="language-sql">CAST(GETDATE() AS DATE)</code>

This approach is efficient and directly returns a DATE data type.

Index Optimization

Crucially, applying functions or CAST operations within WHERE clauses can hinder index utilization, impacting query performance. Avoid such practices whenever possible to maintain optimal query speed.

Recommendation

Considering performance and adaptability, the recommended method for removing the time component from datetime fields in SQL Server is:

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

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