Resolving the Error converting datatype nvarchar to numeric in SQL Server

Learn how to fix the common error `Error converting datatype nvarchar to numeric` in SQL Server when working with tables that contain a mix of text and numeric data.
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Troubleshooting SQL Server: Error Converting Datatype nvarchar to Numeric

When working with SQL Server, you may encounter a frustrating error message: Error converting datatype nvarchar to numeric. This error often arises when you attempt to perform arithmetic operations on nvarchar fields that contain non-numeric values. In this guide, we will explore this problem and present a solution to help you efficiently manage your data conversions.

Understanding the Problem

The issue typically occurs in scenarios where columns are defined as nvarchar but contain numeric values, alongside possible non-numeric entries such as text. For instance, consider a table with two columns (Amount1 and Amount2), where some entries are valid numeric values (like 100 or 200), while others contain letters or may be blank (like A).

Sample Table Data

Amount1Amount2Expected Result1002004.17%A500500B201001.67%When trying to select results across the entire table for a specific calculation, you may receive the error message mentioned above, which stops the query from executing properly.

The SQL Statements Causing the Error

Successful query for a single row:

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Failing query for all rows:

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In the second case, the presence of non-numeric characters in either Amount1 or Amount2 results in the conversion error.

The Solution: Using TRY_CAST or TRY_CONVERT

To effectively handle this error, we can employ the TRY_CAST function (or alternatively, TRY_CONVERT). These functions allow conversions that return NULL for rows where the conversion fails, preventing the entire query from failing.

Implementation Steps

Replacing CAST with TRY_CAST:

Instead of using:

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Use:

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When the conversion cannot be performed, it will return NULL instead of throwing an error.

Using Conditional Logic:

Begin your SQL statement with a CASE structure that checks if the values are valid for conversion:

[[See Video to Reveal this Text or Code Snippet]]

Final SQL Query

Putting it all together, your final query should look similar to this:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

In conclusion, the Error converting datatype nvarchar to numeric in SQL Server can be resolved with a smarter approach to type conversion. By using TRY_CAST and incorporating checks into your SQL statements, you can manage non-numeric entries without experiencing query failures. This method helps maintain data integrity and ensures that you can work with mixed data types effectively.

Next time you encounter this error, remember that a few small changes in your SQL queries can lead to seamless calculations and risk-free data handling.