Sql Server

Escaping the Underscore Character in SQL Server

Introduction

SQL Server uses special characters to execute wildcard searches — one of these characters is the underscore (_). While this character can be incredibly useful for matching single characters in a string, there are instances when you might need to search for the underscore itself. If you find yourself writing a query to find usernames ending with _d, for example, you might be confused about how to correctly escape that underscore. This blog post will explain how to handle this situation effectively.

Understanding the Problem

When you write a query like this:

WHERE Username LIKE '%_d'

this SQL statement would actually search for any usernames that have any single character preceding the letter “d.” If you’re trying to find usernames that literally end with _d, you need to escape that underscore so SQL Server treats it as a regular character, not as a wildcard.

Escaping the Underscore in SQL Server

Using Brackets

To correctly escape the underscore character in SQL Server, you can enclose it in brackets []. This tells SQL Server that you are looking for the underscore character as a literal and not as a wildcard. Here’s how to modify your query:

WHERE Username LIKE '%[_]d'

Explanation

  • Brackets Usage: When you place the underscore within brackets, it signifies to SQL Server that you’re interested in the underscore as a character, not as a wildcard that matches any single character.

  • The Query Breakdown:

    • % before the underscore indicates that there can be any sequence of characters before it.
    • [_] means you’re looking for the underscore character specifically.
    • d remains unchanged, indicating it comes after the underscore.

Additional References

For more detailed information about using wildcard characters and how to implement them as literals in your SQL queries, you can explore the T-SQL Reference for LIKE. This documentation provides additional examples and scenarios on utilizing wildcard characters in SQL Server.

Conclusion

In conclusion, escaping the underscore character in SQL Server is straightforward once you understand the use of brackets. By enclosing the underscore in brackets, you can effectively query your database for exact matches that include the underscore. This technique is vital for accurate data retrieval and ensuring your queries return the expected results. Now you’re equipped to search for usernames or any string that includes the underscore character as needed!

If you have any questions or need further assistance with SQL queries, feel free to comment below!