Escape Single Quote in SQL Server [4 Methods]


SQL

Escaping single quotes in SQL is necessary once you want to include a literal single quote character (') in a string within your SQL queries. This is particularly important to handle correctly so as to prevent syntax errors and guard against SQL injection attacks.

 

List of methods to escape single quote in SQL Server

Listed below are the common methods of escaping single quotes in SQL with explanations and examples for each.

  • Doubling Single Quotes
  • Using the CHAR Function
  • QUOTED_IDENTIFIER Setting
  • Using REPLACE Function

 

1. Doubling Single Quotes

This is the simplest method where you replace a single quote inside a string with two single quotes. This tells SQL Server to treat it as being an actual single quote within the string, instead of treating it as end of the string.

-- Inserting a name with an apostrophe
INSERT INTO Employees (Name) VALUES ('O''Brien');

In this example, doubling the single quote inside the string O'Brien tells SQL Server to treat it as a literal character.

 

2. Using the CHAR Function

You can use the CHAR function with ASCII value 39 representing a single quote. Concatenating parts of string around CHAR(39) forms complete string with single quotes in this method.

-- Inserting a name using the CHAR function for the apostrophe
INSERT INTO Employees (Name) VALUES ('O' + CHAR(39) + 'Brien');

Here, CHAR(39) is used to include a single quote character as part of the string.

 

3. QUOTED_IDENTIFIER Setting

Enclosing string literals with double quotes can be done by setting QUOTED_IDENTIFIER to OFF. This approach enables one include single quotes within the string without needing any escape characters however it changes how double quotes are interpreted by SQL Server and may affect compliance or compatibility with standards of different versions ANSI/ISO standard for Structured Query Language.

-- Using QUOTED_IDENTIFIER setting
SET QUOTED_IDENTIFIER OFF;
INSERT INTO Employees (Name) VALUES ("O'Brien");
SET QUOTED_IDENTIFIER ON;

This method involves temporarily turning off the QUOTED_IDENTIFIER setting to allow double quotes to enclose string literals, which lets single quotes be included without escaping.

 

4. Using REPLACE Function

Although more commonly used when there is need for dynamic replacements across multiple instances within strings, REPLACE function can substitute single quotes with another character or sequence depending on what query requires. It is versatile enough that it works across different SQL platforms.

-- Example of using REPLACE to handle an input string dynamically
DECLARE @name NVARCHAR(50) = 'O''Brien';
SET @name = REPLACE(@name, '''', '''''');
INSERT INTO Employees (Name) VALUES (@name);

The example above shows how to use REPLACE to duplicate single quotes in a variable. This is very helpful when the input is dynamic or when processing a batch of names that may have apostrophes.

 

Summary

Escaping single quotes in SQL is the way to go when it comes to handling queries that contain string data with apostrophes. This practice is necessary for avoiding syntax mistakes and protecting against SQL injection vulnerabilities. Doubling the single quotes within a string is the most popular method across different SQL database systems. In this approach, every occurrence of a single quote (') should be replaced by two single quotes ('') so that it can be treated as a literal character rather than a string delimiter.

Another method, which is specifically useful in SQL Server, involves using the CHAR function with the ASCII value 39 to insert a single quote character. This comes in handy during dynamic SQL constructions or when concatenating strings that require direct text manipulation.

For environments like SQL Server where settings are adjustable, there is an option called QUOTED_IDENTIFIER which allows SQL developers to choose how single and double quotes are interpreted. When this setting is turned off, strings can be enclosed in double quotes thereby treating any single quotes within those strings as regular characters without having to escape them.

Moreover, the REPLACE function offers flexibility when dealing with strings containing single quotes by enabling dynamic substitution of such quotes with another character or sequence of characters. This can be very helpful in larger more complex SQL operations or while processing data inputs which may not follow standardization rules.

 

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Deepak Prasad

Deepak Prasad

He is the founder of GoLinuxCloud and brings over a decade of expertise in Linux, Python, Go, Laravel, DevOps, Kubernetes, Git, Shell scripting, OpenShift, AWS, Networking, and Security. With extensive experience, he excels in various domains, from development to DevOps, Networking, and Security, ensuring robust and efficient solutions for diverse projects. You can connect with him on his LinkedIn profile.

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