Fixing 'Conversion Failed' Errors: How to Properly Convert Varchar Value to Data Type Int

Learn how to fix the common error, "Conversion failed when converting the varchar value to data type int," by properly converting varchar values to integer data types in SQL Server.

Table of Contents

1. Introduction
2. Causes of Conversion Failed Errors
3. Step-by-Step Solution
4. Frequently Asked Questions (FAQs)
5. Related Resources

Introduction

In SQL Server, data type conversions are a common task when querying or manipulating data. Sometimes, you may encounter an error while converting a varchar value to an integer data type. This error message is:

Conversion failed when converting the varchar value 'SampleValue' to data type int.

This guide will help you understand the causes behind this error and provide a step-by-step solution to properly convert varchar values to integer data types.

Causes of Conversion Failed Errors

The primary cause of this error is attempting to convert a non-numeric varchar value to an integer data type. Other possible causes include:

1. Incorrect syntax in the CONVERT or CAST functions
2. Incorrect data type specified in the conversion
3. Varchar value containing non-numeric characters

Step-by-Step Solution

To fix the "Conversion failed when converting the varchar value to data type int" error, follow these steps:

Step 1: Identify the varchar value causing the error

• Inspect the data in the varchar column and find the non-numeric values that are causing the error.

Step 2: Use the TRY_CONVERT or TRY_CAST functions

• The TRY_CONVERT and TRY_CAST functions return a NULL value if the conversion fails, instead of throwing an error.

Example:

SELECT TRY_CONVERT(int, VarcharColumn) AS ConvertedValue
FROM TableName

OR

SELECT TRY_CAST(VarcharColumn AS int) AS ConvertedValue
FROM TableName

Step 3: Filter out the non-numeric values (Optional)

• If you want to exclude the non-numeric values from the result, you can use the ISNUMERIC function.

Example:

SELECT TRY_CONVERT(int, VarcharColumn) AS ConvertedValue
FROM TableName
WHERE ISNUMERIC(VarcharColumn) = 1

Frequently Asked Questions (FAQs)

What is the difference between CONVERT and CAST functions?

CONVERT and CAST are both used to convert an expression from one data type to another in SQL Server. CONVERT is a more flexible function, allowing for custom formatting options, while CAST is an ANSI SQL-92 compliant function with a simpler syntax.

Can I use TRY_PARSE instead of TRY_CONVERT or TRY_CAST?

Yes, TRY_PARSE is another function that can be used to convert a varchar value to an integer data type. However, TRY_PARSE requires the USING clause to specify the culture argument, and it's more suitable for converting date and time values from a varchar value.

What if I need to handle non-numeric values differently?

You can use a CASE statement in combination with the ISNUMERIC function to handle non-numeric values differently. For example:

SELECT CASE
         WHEN ISNUMERIC(VarcharColumn) = 1 THEN TRY_CONVERT(int, VarcharColumn)
         ELSE -1
       END AS ConvertedValue
FROM TableName

How can I find out which rows are causing the conversion error?

You can use the ISNUMERIC function to filter the varchar values that cannot be converted to an integer data type. Example:

SELECT VarcharColumn
FROM TableName
WHERE ISNUMERIC(VarcharColumn) = 0

How can I remove non-numeric characters from a varchar value before converting it to an integer?

You can use a user-defined function or a combination of built-in string functions to remove non-numeric characters from the varchar value before converting it to an integer.

Related Resources

1. Official Microsoft Documentation for CONVERT and TRY_CONVERT
2. Official Microsoft Documentation for CAST and TRY_CAST
3. Official Microsoft Documentation for TRY_PARSE
4. Guide to Using SQL Server String Functions
5. Handling Errors in SQL Server with TRY-CATCH