How to Efficiently Compare Datetime Values with Only the Date Part in SQL Server?

Comparing Datetime Values with Only Date in SQL Server

When querying a database for records created on a specific date, it's important to consider the datetime nature of the column. Comparing a datetime field with only the date part using the equals operator (e.g., U.DateCreated = '2014-02-07') may not return the expected results.

Solution 1: Using Date Ranges

To accurately compare a datetime field with only the date part, use a date range:

Select * from [User] U
where U.DateCreated >= '2014-02-07' and U.DateCreated < dateadd(day,1,'2014-02-07')

This approach ensures that records created on '2014-02-07' are retrieved, regardless of the time component.

Reason for Avoiding Functions in WHERE Clause

It's not recommended to use functions (e.g., convert) in the WHERE clause for two main reasons:

1. Loss of Index Optimization: Functions on data may prevent the optimizer from using indexes, resulting in slower queries.
2. High Computational Overhead: Functions can introduce significant computational overhead when applied to large datasets.

Best Practice for Date Ranges

For optimal performance and accuracy when querying date and time ranges, it is best practice to use the following format:

WHERE col >= '20120101' AND col < '20120201'

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