How Can I Efficiently Truncate Datetimes in SQL Server?

SQL Server Datetime Truncation: Best Practices and Methods

Removing the time portion from a datetime value is a frequent task in SQL Server. This guide explores various techniques, highlighting their strengths and weaknesses.

The Recommended Approach: Leveraging the CAST Function (SQL Server 2008 and later)

For SQL Server 2008 and subsequent versions, the CAST function provides the simplest and most reliable solution:

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

This approach is both efficient and adheres to ANSI standards, ensuring compatibility and predictability.

The Standard Method (Pre-SQL Server 2008)

Before SQL Server 2008, the DATETIMEADD function was the preferred method:

<code class="language-sql">DATEADD(DD, DATEDIFF(DD, 0, getdate()), 0)</code>

This calculates the difference in days from a reference date (0) and adds it back, effectively removing the time component.

A Faster, but Less Reliable Option

A faster alternative, though less portable and potentially prone to changes in future SQL Server versions, involves casting to and from a float:

<code class="language-sql">CAST(FLOOR(CAST(your_datetime_column AS FLOAT)) AS DATETIME)</code>

This method exploits the internal binary representation of datetime values. However, its reliance on implementation details makes it less robust.

The Method to Avoid: Using CONVERT

Using CONVERT to truncate datetimes is generally discouraged. Its reliance on string conversions introduces inefficiency and potential locale-related issues:

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

Performance Optimization

The CAST method (available since SQL Server 2008) is generally the most efficient. However, the most effective strategy is to minimize the need for datetime truncation through careful database design and query optimization.

The above is the detailed content of How Can I Efficiently Truncate Datetimes in SQL Server?. For more information, please follow other related articles on the PHP Chinese website!