How to escape a single quote in SQL

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When handling user inputs in SQL queries, I’ve encountered issues with single quotes in text fields causing SQL errors. What is the recommended way to escape single quotes to prevent SQL errors and avoid injection vulnerabilities?

If someone could provide examples of escaping single quotes properly across different SQL databases, that would be great.
Nov 11 in Cyber Security & Ethical Hacking by Anupam
• 5,550 points
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1 answer to this question.

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Escaping single quotes in SQL is crucial to prevent SQL syntax errors and, more importantly, to avoid SQL Injection vulnerabilities when handling user inputs. The method to escape single quotes can vary slightly depending on the SQL database management system (DBMS) you are using.

1. SQL Standard

Double the single quote.

Example: If your input is John's, you would escape it as John''s.

SELECT * FROM users WHERE name = 'John''s';

2. MySQL

Method 1: Use parameterized queries or prepared statements. This is the most secure method against SQL injection.

-- Using a parameter (pseudo-example, actual syntax may vary based on programming language)
PREPARE stmt FROM 'SELECT * FROM users WHERE name = ?';
SET @name = 'John''s';  -- Though parameterization handles quoting
EXECUTE stmt USING @name;

Method 2: Double the single quote, as per the SQL standard.

SELECT * FROM users WHERE name = 'John''s';

Method 3: Use backslash before the single quote

SELECT * FROM users WHERE name = 'John\'s';

3. PostgreSQL

Method 1: Parameterized queries or prepared statements.

PREPARE stmt FROM 'SELECT * FROM users WHERE name = $1';
EXECUTE stmt ('John''s');

Method 2: Double the single quote.

SELECT * FROM users WHERE name = 'John''s';

Method 3: This method is more about avoiding the need to double single quotes within the specific string literal, rather than escaping them.

SELECT * FROM users WHERE name = $$John's$$;

4. Microsoft SQL Server

Method 1: Use parameterized queries.

DECLARE @name nvarchar(50) = 'John''s';
EXEC sp_executesql N'SELECT * FROM users WHERE name = @name', N'@name nvarchar(50)', @name = @name;

Method 2: Double the single quote.

SELECT * FROM users WHERE name = 'John''s';

5. Oracle

Method 1: Use bind variables

VARIABLE name VARCHAR2(50);
EXEC :name := 'John''s';
BEGIN
  FOR rec IN (SELECT * FROM users WHERE name = :name) LOOP
    -- Process record
  END LOOP;
END;

Method 2: Double the single quote.

SELECT * FROM users WHERE name = 'John''s';
answered Nov 11 by CaLLmeDaDDY
• 8,390 points

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