How to Remove Unusual Characters from a SQL Server VARCHAR Column?

Remove unusual characters from SQL Server VARCHAR columns

Background:

Certain non-standard characters, especially characters with diacritics (such as a with a hat), are stored in SQL Server varchar columns. This issue arises from limited control over the import of the .csv data source.

Solution:

Option 1: Use .NET regular expressions

In C#, you can use regular expressions to remove these characters. You can use the String.Replace method as shown below:

<code class="language-csharp">Regex.Replace(s, @"[^\u0000-\u007F]", string.Empty);</code>

Option 2: Create SQL CLR function

Since SQL Server does not natively support regular expressions, you can create a SQL CLR function. This requires:

• Create a .NET class library project in Visual Studio
• Use regular expressions to implement the Replace function
• Build the project and add the assembly to the SQL Server database
• Create a SQL CLR function that wraps a .NET function

Implementation:

Option 1:

<code class="language-csharp">Regex.Replace(inputString, @"[^\u0000-\u007F]", string.Empty);</code>

Option 2:

• Create a .NET class called StackOverflow with the following code:

<code class="language-csharp">[SqlFunction(DataAccess = DataAccessKind.None, IsDeterministic = true, Name = "RegexReplace")]
public static SqlString Replace(SqlString sqlInput, SqlString sqlPattern, SqlString sqlReplacement)
{
    string input = (sqlInput.IsNull) ? string.Empty : sqlInput.Value;
    string pattern = (sqlPattern.IsNull) ? string.Empty : sqlPattern.Value;
    string replacement = (sqlReplacement.IsNull) ? string.Empty : sqlReplacement.Value;
    return new SqlString(Regex.Replace(input, pattern, replacement));
}</code>

• Build the project and add the assembly to the SQL Server database
• Create SQL CLR function:

<code class="language-sql">CREATE FUNCTION [dbo].[StackOverflowRegexReplace] (@input NVARCHAR(MAX),@pattern NVARCHAR(MAX), @replacement NVARCHAR(MAX))
RETURNS NVARCHAR(4000)
AS EXTERNAL NAME [StackOverflow].[StackOverflow].[Replace]
GO</code>

• Usage example:

<code class="language-sql">SELECT [dbo].[StackOverflowRegexReplace] ('Hello Kitty Essential Accessory Kit', '[^\u0000-\u007F]', '')</code>

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