How to Safely Match Escaped Strings Using LIKE in PostgreSQL?

Matching Escaped Strings in PostgreSQL

In PostgreSQL, using the LIKE operator to match patterns can become problematic when dealing with special characters like '_' and '%'. These characters can match wildcards, leading to unintended results. To ensure literal matching, it's essential to escape them properly.

The escape character used for LIKE is typically the backslash (), which should be repeated twice to represent a single escape character in the pattern. For example, "rob_" would escape the '_' character, allowing it to match only strings that literally start with "rob_". However, in PostgreSQL 9.1, the default escape character can change depending on the standard_conforming_strings setting.

To avoid potential issues, it's recommended to use the REPLACE function to substitute special characters with their escaped equivalents on the server-side. This approach is safer than handling the escaping on the client-side, as it eliminates the need for additional user input validation.

For example, the following query would replace all instances of '_' and '%' with their escaped counterparts and then perform the LIKE comparison, ensuring that the pattern is matched literally:

SELECT * FROM users WHERE name LIKE replace(replace(replace(,'^','^^'),'%','^%'),'_','^_') ||'%' ESCAPE '^'

By utilizing server-side replacements, you can ensure accurate and unambiguous pattern matching while avoiding potential security vulnerabilities.

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