Why Does SQL Server Lose Milliseconds When Storing Datetime Values?

Missing milliseconds in SQL Server: Understanding the granularity of time storage

When working with time-sensitive data in SQL Server, it is important to be aware of the limitations of storing and processing milliseconds. Among the questions raised by users was an issue regarding missing milliseconds when inserting datetime values ​​into a table.

Question:

The user creates a table with a datetime column and executes an insert statement with a datetime value containing milliseconds. However, when retrieving the value, the millisecond component seems to disappear.

Explanation:

SQL Server itself stores time at approximately 1/300th of a second granularity, which is consistent with 0, 3, and 7 millisecond intervals. For example, the increment is:

• 00:00:00.000
• 00:00:00.003
• 00:00:00.007
• 00:00:00.010
• 00:00:00.013

In the given scenario, the datetime value contains a millisecond component at a granularity that SQL Server does not support. Therefore, when the value is stored in the table, it is rounded to the nearest 1/300th of a second, resulting in a loss of millisecond precision.

Solution:

To achieve millisecond precision in SQL Server, an alternative approach is required:

• Custom numeric field storage: Convert a datetime value to a custom numeric field and reconstruct it on retrieval.
• String Storage: Stores a datetime value as a string in a known format. This can accommodate milliseconds, but introduces conceptual complexity.

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