How to Correctly Match Date-Only Queries with DateTime Fields in SQL Server?

Matching Date-only Queries with Datetime Fields in SQL Server

When querying datetime fields in SQL Server using date-only values, it's essential to understand the implications to ensure accurate results.

In the provided example:

Select * from [User] U
where  U.DateCreated = '2014-02-07'

If the user was created at '2014-02-07 12:30:47.220,' the query will return no results because it only compares exactdatetime values.

Recommended Approach

To resolve this issue and accurately match date-only values with datetime fields, it's recommended to use the following approach:

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

This query specifies a range that includes all records with a datetime value of '2014-02-07' or later but before '2014-02-08.'

Importance of SARGable Predicates and Avoiding Functions

It's crucial to avoid using functions like convert() in the where clause when comparing datetime values with date-only criteria. This can hinder index usage, slow down queries, and introduce unnecessary calculations. Instead, modifying the query to suit the data (also known as using SARGable predicates) enhances query performance.

Best Practices for Date Range Queries

Furthermore, it's advisable to avoid using the BETWEEN operator when querying date ranges. Instead, use the following form for optimal results:

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

This approach ensures compatibility with all data types and precisions and eliminates potential issues with the time component of datetime values.

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