TSQL Remove Special Characters

Why Remove Special Characters?

Removing special characters from strings is a common data cleaning task in SQL Server. It’s crucial for:

• Data Consistency: Standardizing data from different sources ensures uniformity. For example, phone numbers might have varying formats (e.g., “123-456-7890” vs. “1234567890”). Removing non-numeric characters allows for consistent storage and analysis.
• Preventing SQL Injection: Sanitizing user input by removing potentially harmful characters can help mitigate SQL injection vulnerabilities. If user input is used in dynamic SQL, special characters can alter the intended query, leading to security risks.
• Data Analysis and Reporting: Special characters can interfere with data analysis and reporting. For example, if you’re counting distinct values, strings with subtle differences due to special characters might be counted as separate entries.
• Data Integration: When transferring data between systems, special characters can cause errors or inconsistencies. Cleaning the data beforehand ensures smooth integration.

Real World Examples:

• A company importing customer data from a CSV file might use this function to remove stray characters from addresses or names.
• An e-commerce website could use it to clean product descriptions before storing them in a database, ensuring consistent search results.
• A financial application might use this to sanitize user entered amounts, removing currency symbols, or commas, before storing the numerical value.

The Function

Usage: Select dbo.StripSpecialChars(‘abc12+=\34def’); returns abc1234def

Create Function [dbo].[StripSpecialChars](@Temp VarChar(1000))
Returns VarChar(1000)
AS
Begin

    Declare @KeepValues as varchar(50)
    Set @KeepValues = '%[^a-zA-Z0-9 ]%'
    While PatIndex(@KeepValues, @Temp) > 0
        Set @Temp = Stuff(@Temp, PatIndex(@KeepValues, @Temp), 1, '')

    Return @Temp
End

Adjust the @KeepValues as needed. Or if you want to get fancy, add it as a second input variable.

Explanation of PatIndex and Stuff:

• PatIndex(@KeepValues, @Temp): This function searches for the first occurrence of the pattern defined in @KeepValues within the @Temp string. In this case, @KeepValues defines a pattern that matches any character that is not an uppercase or lowercase letter, a digit, or a space. If a match is found, PatIndex returns the starting position of the match; otherwise, it returns 0.
• Stuff(@Temp, PatIndex(@KeepValues, @Temp), 1, ”): This function modifies the @Temp string. It takes four arguments:
  • The string to modify (@Temp).
  • The starting position of the characters to replace (obtained from PatIndex).
  • The number of characters to replace (1, in this case, to remove one special character).
  • The replacement string (an empty string ”, effectively deleting the character).

In essence, the While loop repeatedly finds and removes special characters until none remain.