Resolving SQL Server Conversion Errors: A Comprehensive Guide to nvarchar to int Issues

Understand why you face conversion errors in SQL Server and learn effective solutions to fix `nvarchar` to `int` conversion failures in your functions.
---

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: SQL Server function errors trying to run. Throws conversion failed error

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Resolving SQL Server Conversion Errors: A Comprehensive Guide to nvarchar to int Issues

Introduction

If you're developing with SQL Server and have encountered frustrating conversion errors when executing your custom functions, you're definitely not alone. A common error developers face is the infamous "conversion failed when converting the nvarchar value '0.5' to data type int." In this guide, we'll explore why these conversion errors occur and how you can fix them in your SQL Server function.

Understanding the Problem

In SQL Server, data types have inherent properties that dictate how they can interact with one another. When the SQL Server engine needs to perform an operation involving multiple data types, it engages a process called data type precedence. Specifically, if one operand is of type int and the other is nvarchar, the SQL Server will attempt to convert the nvarchar to int, leading to potential errors like the one we're facing.

The Error Message

The specific error message that indicates a issue can be seen as follows:

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

This suggests that SQL Server is trying to convert a non-integer value ('0.5') into an integer, which causes the conversion error.

Analyzing the Function Code

Looking at your SQL function code, the issue primarily arises in these CASE statements within the assignments for pos_Sort1 and pos_Sort2:

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

In both cases, the ELSE clause is returning an int (1 or 2) while the THEN clause returns a nvarchar. This unintentional mixing of data types is what's causing the conversion error.

Solution: How to Fix the Conversion Error

There are a couple of straightforward paths to resolve this problem. Let's break them down:

Option 1: Enclose integers in single quotes

The simplest resolution to the conversion issue is to treat the integers (1 and 2) as strings by enclosing them in single quotes:

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

Option 2: Use TRY_CAST

Alternatively, you could use TRY_CAST to safely convert the substring expressions to int. This method is beneficial because if the conversion fails (for example, if the substring represents an invalid integer), it will return NULL instead of an error:

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

This way, you safely manage any conversion issues.

Streamlining Your Function

Beyond resolving the conversion error, it’s worth noting that, should you be using a multi-statement table valued function, you might want to consider switching to an inline table valued function (iTVF). Inline table valued functions tend to perform better, especially when used in a correlated context.

Here’s a revised version of your SQL function using some suggested improvements:

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

Conclusion

When dealing with SQL Server, it's essential to ensure that you're managing data types correctly to avoid conversion errors. By either enclosing your integers in quotes or utilizing TRY_CAST, you can mitigate these issues effectively. Additionally, moving to an inline table-valued function can optimize your SQL performance. Happy coding!