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

Optimizing DateTime Data: Removing the Time Component in SQL Server

Challenge:

Processing large SQL Server datasets often requires efficient removal of the time component from datetime fields. Two common techniques are frequently employed:

• DATEADD(dd, DATEDIFF(dd, 0, getdate()), 0)
• CAST(CONVERT(CHAR(11), getdate(), 113) AS DATETIME)

Optimal Approach:

Performance benchmarks consistently show DATEADD(dd, DATEDIFF(dd, 0, getdate()), 0) as the most efficient method. This approach:

• Minimizes resource consumption, as confirmed by CPU profiling.
• Offers flexibility for calculations like determining the first day of the month or the following day by adjusting the final "0" parameter.

Modern SQL Server versions (2008 and later) provide superior alternatives:

• Direct DATE Casting: CAST(getdate() AS DATE) directly converts the datetime to a date data type, eliminating the need for time component removal.
• DATETIME2 Data Type: For datetime2 fields, the DATEADD method remains applicable, but requires adjusting the epoch value:

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

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

Key Considerations:

• Index Impact: Using these functions within WHERE clauses can negatively impact index utilization. Careful consideration is necessary.
• Data Format Sensitivity: The CAST(CHAR()) method's reliance on character conversion introduces potential vulnerabilities related to language settings and date formats.
• Data Type Selection: Avoid using FLOAT for storing dates due to its internal representation, which may not be optimal for large datasets.

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