Unlocking the Power of LIKE: A Beginner's Guide to Safe String Escaping in SQL Server
Escaping Strings for Safe LIKE Expressions in SQL Server (T-SQL)
%
: Percent sign - Matches any single character.[]
: Square brackets - Used to define a set of characters to match.-
: Hyphen - Represents a range of characters within square brackets (e.g.,[a-z]
).
Escaping with Backslash:
To prevent these characters from being interpreted as special operators, you need to escape them using a backslash (\
) character before the specific character.
Example:
Imagine you want to search for names containing the literal character %
. Without escaping, the query:
SELECT * FROM Customers WHERE Name LIKE '%';
would return all names in the Customers
table, regardless of their content, because %
acts as a wildcard, matching any character sequence.
To search for names containing the literal %
, you need to escape it:
SELECT * FROM Customers WHERE Name LIKE '\%';
This query will now correctly search for names with the exact character %
.
Alternative: Square Brackets for [
and ]
For the characters [
and ]
, you can alternatively enclose them within square brackets to treat them as literal characters. This approach avoids the need for escaping with a backslash:
SELECT * FROM Customers WHERE Name LIKE '[%]';
Best Practices:
- Always escape special characters when using them as literal values within the
LIKE
pattern. - Consider using parameterized queries to prevent SQL injection vulnerabilities. Parameterized queries separate the data from the T-SQL code, making it safer and more secure.
- Be mindful of the context: If you're unsure whether a character needs escaping, it's generally better to err on the side of caution and escape it.
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