How Can I Perform Literal Pattern Matching in PostgreSQL Queries to Avoid Unintentional Broadening of Search Results?

Literal Pattern Matching in PostgreSQL Queries

In PostgreSQL, performing LIKE pattern matching on string columns requires special attention when dealing with user-provided input. Unvalidated input containing special characters (e.g., '_' or '%') can unintentionally broaden the search results. To address this issue, it's necessary to ensure that these characters are interpreted literally.

Client-Side or Server-Side Escaping

The decision of whether to handle escaping on the client-side or server-side depends on specific requirements. Client-side escaping involves pre-processing user input in the application code before sending it to the database. This approach provides more control but requires additional handling logic.

Server-Side Escaping

PostgreSQL offers a more elegant solution for server-side escaping. By using the ESCAPE clause in the LIKE statement, you can specify a special character to be used for quoting wildcard characters. This prevents them from being interpreted as regex metacharacters.

For example, the following query would match the exact string "rob":

SELECT * FROM users WHERE name LIKE 'rob%' ESCAPE '^'

Escaping Considerations

When using server-side escaping, it's important to consider the following:

• Default Escape Character: The default escape character is the backslash (), but it can be changed with the ESCAPE clause.
• Double Escaping: To match a single escape character literally, it must be escaped twice (e.g., 'rob^%node1^^node2.uucp@%' ESCAPE '^').
• Non-Standard Conforming Strings: In previous PostgreSQL versions where standard_conforming_strings is OFF, the backslash escape character might be used for other purposes. In such cases, it's advisable to use an alternative quote character.
• SQL Injection: When using server-side escaping, it's crucial to sanitize user input to prevent SQL injection.

Go-PGSQL Example

For Go-PGSQL, you can use the following query to perform literal pattern matching:

db.Query("SELECT * from USERS where name like replace(replace(replace(,'^','^^'),'%','^%'),'_','^_') ||'%' ESCAPE '^'",
variable_user_input);

This query uses server-side replacement to escape wildcard characters, an alternative escape character, and double escaping to ensure literal matching while safeguarding against SQL injection.

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