SQL Server Date vs DateTime

As a senior developer working with SQL Server, I have frequently used date and datetime data types. In this article, I’ll walk you through everything you need to know about SQL Server’s date and time data types, with a special focus on the differences between the DATE and DATETIME data types.

SQL Server offers several data types for storing temporal data, each with its own characteristics, precision, and storage requirements. Choosing the right data type is crucial for both data integrity and system performance.

Date/Time Data Types in SQL Server

When SQL Server first launched, DATETIME was the primary option for storing date and time values. However, starting with SQL Server 2008, Microsoft introduced DATETIME2, which offers more features and greater flexibility than its predecessor.

DATE vs DATETIME

Let’s break down the fundamental differences between these two common data types.

DATE Data Type

The DATE data type was introduced in SQL Server 2008 and stores only date information (year, month, day) without any time component.

Key characteristics

Stores date values only (no time component)
Range: January 1, 0001 to December 31, 9999
Storage size: 3 bytes
Format: YYYY-MM-DD
No fractional seconds precision (because it doesn’t store time)

Check out SQL Server Date Data Types

DATETIME Data Type

DATETIME has been around since early versions of SQL Server and stores both date and time information.

Key characteristics:

Stores both date and time values
Range: January 1, 1753 to December 31, 9999
Storage size: 8 bytes
Accuracy: rounded to increments of .000, .003, or .007 seconds
Default format: YYYY-MM-DD hh:mm.nnn

DATETIME2

When comparing DATE and DATETIME, it’s also essential to consider DATETIME2, which offers additional features beyond the older DATETIME. If you’re working with SQL Server 2008 or newer, DATETIME2 is often the better choice over DATETIME.

Key advantages of DATETIME2:

Larger date range (January 1, 0001 to December 31, 9999)
User-defined precision (0 to 7 decimal places for seconds)
Variable storage size (6 to 8 bytes, depending on precision)
More consistent behavior with ISO-8601 format standards

Storage and Range Comparison

Here’s a table comparing the key attributes of these data types:

Feature	DATE	DATETIME	DATETIME2
Storage Size	3 bytes	8 bytes	6-8 bytes (depends on precision)
Date Range	0001-01-01 to 9999-12-31	1753-01-01 to 9999-12-31	0001-01-01 to 9999-12-31
Time Component	No	Yes	Yes
Time Precision	N/A	3.33ms	100ns (with precision 7)
Format	YYYY-MM-DD	YYYY-MM-DD hh:mm.nnn	YYYY-MM-DD hh:mm.nnnnnnn

When to Use DATE vs DATETIME

DATE

You only need to store the date without time information
You want to save storage space (DATE uses 3 bytes vs. DATETIME’s 8 bytes)
You need to perform date-only comparisons
You’re storing birth dates, anniversaries, or other date-only values

DATETIME

You need to store both date and time components
You’re working with legacy applications that expect DATETIME
You need compatibility with older versions of SQL Server (pre-2008)
The precision limitations (3.33ms) are acceptable for your application

DATETIME2

You need greater precision than DATETIME offers
You need dates earlier than 1753
You want more consistent behavior with ISO-8601 formatting
Storage size optimization is important (with lower precision settings)

Practical Examples

Let’s look at some practical examples of how to work with these data types in SQL Server.

Creating Tables with Date and DateTime Columns

Example 1:

Creating a table with a DATE column using the below query.

CREATE TABLE CustomerBirthdays (
    CustomerID INT PRIMARY KEY,
    CustomerName VARCHAR(100),
    BirthDate DATE
);

After executing the above query, the table with the date data type column was created successfully, as shown in the screenshot below.

Let me insert a record into the above table using the below query.

INSERT INTO CustomerBirthdays (CustomerID, CustomerName, BirthDate)
VALUES (1, 'Steve Smith', '1985-07-17');

After executing the above query, I got the expected output as shown in the screenshot below.

Example 2:

Let us create a table with a datetime column.

CREATE TABLE OrderDetails (
    OrderID INT PRIMARY KEY,
    ProductID INT,
    OrderDateTime DATETIME,
    Quantity INT
);

The table was created successfully after executing the above query, as shown below.

Let me insert a record into the new table using the following query.

INSERT INTO OrderDetails (OrderID, ProductID, OrderDateTime, Quantity)
VALUES (1001, 5, '2023-11-25 14:30:00', 10);

After executing the above query, I obtained the expected output, as shown in the screenshot below.

Date Format Considerations

When working with DATE and DATETIME, it’s important to understand format considerations. The ISO-8601 format behavior differs between these types. For DATETIME (the older type), you often need to use YYYYMMDD format without dashes to ensure consistent behavior across different language settings.

For DATE or DATETIME2, the proper ISO 8601 format (YYYY-MM-DD) is consistently supported, regardless of language settings.

Date and Time Functions in SQL Server

SQL Server provides numerous functions for working with date and time values.

GETDATE() – Returns the current database system timestamp as a DATETIME value
CURRENT_TIMESTAMP – SQL standard equivalent of GETDATE()
SYSDATETIME() – Returns the date and time of the system on which SQL Server is running (higher precision)
DATEADD() – Adds a specified time interval to a date
DATEDIFF() – Returns the difference between two dates
DATEPART() – Returns a specified part of a date (like year, month, day)
FORMAT() – Formats date and time values according to specified formats

Examples

We can execute the following queries to get the expected outputs.

-- Get current date only
SELECT CAST(GETDATE() AS DATE) AS CurrentDate;

-- Add 30 days to a date
SELECT DATEADD(DAY, 30, '2023-11-25') AS DatePlus30Days;

-- Get difference between two dates in days
SELECT DATEDIFF(DAY, '2023-01-01', '2023-12-31') AS DaysDifference;

-- Extract year from a date
SELECT DATEPART(YEAR, GETDATE()) AS CurrentYear;

-- Format a date as MM/DD/YYYY (US format)
SELECT FORMAT(GETDATE(), 'MM/dd/yyyy') AS FormattedDate;

After executing the above queries, I obtained the expected output, as shown in the screenshot below.

Performance Considerations

When working with date and time data in SQL Server, performance is a critical consideration, especially for large databases.

Indexing Date Columns

DATE columns are more efficient to index than DATETIME due to their smaller size
Filtered indexes on date ranges can significantly improve query performance.
Consider using computed columns with date parts (year, month) for frequently queried date component.s

Storage Impact

For large tables with millions of rows, the choice between DATE and DATETIME can have a significant impact on storage requirements.

1 million DATE values: ~3MB
1 million DATETIME values: ~8MB

Best Practices

Below are the best practices

Choose the correct data type for your needs
- Use DATE when you don’t need time information
- Use DATETIME2 instead of DATETIME for new development
- Reserve DATETIME primarily for backward compatibility
Use parameterized queries
- Avoid string literals for dates to prevent SQL injection and conversion issues.
- Let SQL Server handle the conversion from application data types
Be mindful of time zones
- Consider storing UTC and converting to local time in the application
- For SQL Server 2016 and later, explore the AT TIME ZONE feature for time zone conversions
Format dates consistently
- Use ISO 8601 format (YYYY-MM-DD) for date literals in code
- Remember that formats behave differently across data types
Consider business requirements
- For applications needing to record precise timestamps (like financial transactions), use DATETIME2 with appropriate precision
- For applications storing historical dates that might predate 1753, use DATE or DATETIME2

Conclusion

Choosing between DATE and DATETIME in SQL Server is just a technical decision—it affects storage requirements, query performance, and application behavior.

For date-only values, DATE is the clear winner with its smaller footprint and simplified comparison semantics. For date-time values in modern applications, DATETIME2 generally offers more advantages than the legacy DATETIME type.

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Bijay Kumar Sahoo

After working for more than 15 years in the Software field, especially in Microsoft technologies, I have decided to share my expert knowledge of SQL Server. Check out all the SQL Server and related database tutorials I have shared here. Most of the readers are from countries like the United States of America, the United Kingdom, New Zealand, Australia, Canada, etc. I am also a Microsoft MVP. Check out more here.