Have you ever encountered the error message “Implicit conversion from data type datetime to int is not allowed” while working with SQL Server? If so, don’t worry, you’re not alone. In this article, we will explore this error and discuss various solutions to fix it.

Let’s start by understanding the scenario that triggers this error. Consider a situation where you have a table with two columns: ItemID (INT) and IsAvailable (INT). You want to display the current date and time if the IsAvailable column is NULL. To achieve this, you use the ISNULL function in your query:

SELECT ItemID, ISNULL(IsAvailable, GETDATE()) AvailableNow
FROM TestTable;

However, when you execute this query, you encounter the following error:

Msg 257, Level 16, State 3, Line 2
Implicit conversion from data type datetime to int is not allowed.
Use the CONVERT function to run this query.

The error message suggests using the CONVERT function to resolve the issue. Let’s explore the solutions provided in the example and discuss their pros and cons.

Solution 1: Using CONVERT

The first solution involves using the CONVERT function to explicitly convert the IsAvailable column to the datetime data type:

SELECT ItemID, ISNULL(CONVERT(DATETIME, IsAvailable), GETDATE()) AvailableNow
FROM TestTable;

This solution resolves the error, but it introduces a small problem. The IsAvailable column, which is of type INT, is converted to datetime and displays the value of the year 1900. Although this workaround is better than the error itself, it still doesn’t provide accurate results.

Solution 2: Using COALESCE

The second solution involves using the COALESCE function instead of ISNULL:

SELECT ItemID, COALESCE(IsAvailable, GETDATE()) AvailableNow
FROM TestTable;

This solution also fixes the error and avoids the incorrect conversion to datetime. COALESCE returns the first non-null value from the provided arguments, which in this case is the current date and time.

Solution 3: Using CASE Statement

The third solution involves using a CASE statement to handle the NULL value:

SELECT ItemID, CASE WHEN IsAvailable IS NULL THEN GETDATE() ELSE IsAvailable END AvailableNow
FROM TestTable;

This solution provides the same result as the previous one, but it uses a different approach. The CASE statement checks if the IsAvailable column is NULL and returns the current date and time if true, otherwise it returns the original value.

Solution 4: Using CONVERT with VARCHAR

The fourth solution addresses the issue of incorrect data by converting the values to VARCHAR:

SELECT ItemID, CASE WHEN IsAvailable IS NULL THEN CONVERT(VARCHAR(26), GETDATE()) ELSE CONVERT(VARCHAR(26), IsAvailable) END AvailableNow
FROM TestTable;

This solution ensures that the values are displayed correctly without any unwanted conversions. The CONVERT function is used to convert the values to VARCHAR with a length of 26 characters.

Now that we have explored these solutions, you can choose the one that best suits your requirements. It’s important to note that these solutions are not exhaustive, and there might be other approaches to fix this error. If you have any better solutions, feel free to share them with us.

Remember to clean up the temporary table after you have finished testing:

DROP TABLE TestTable;

That’s all for now! We hope this article has helped you understand how to fix the “Implicit conversion from data type datetime to int is not allowed” error in SQL Server. If you have any questions or suggestions, please let us know.