To create and run SQL Statements, applications frequently need to accept user input when working with databases. However, handling user-provided input incorrectly will lead to SQL injection attacks or information breaches. In this blog, let us explore how user input can be added to an SQL Statement.
Table of Contents:
In most applications, managing, updating, and retrieving data from a database depends heavily on user interaction. SQL statements frequently need user input to make applications dynamic and responsive.
- Dynamically retrieving data: People frequently request particular data to obtain customer records, look for products in an online store, or filter reports based on periods.
- User Authentication: Applications must compare stored records in a database with user credentials.
Proper handling of user input in SQL is very important for keeping the security, integrity, and performance of a database-based application intact. These are key reasons why we need to handle the user input properly:
- One of the most serious security flaws that arises when hackers alter user input to run malicious SQL commands is SQL injection.
- Ineffective queries resulting from poorly managed user input can cause the database to lag, which can be solved by using index-based searches.
Master Advanced SQL Skills Today!
Enroll now and transform your future!
Improper handling of user input in SQL can lead to a variety of dangerous security vulnerabilities, data integrity issues, and performance issues.
- Data Corruption: Invalid or inappropriate user input will cause wrong, missing, or distorted data.
- Unauthorized Users: Users can also use poor input handling to access data they are not allowed to view.
There are a few methods in which we can add the user input to an SQL Statement safely, which can be done by using parameterized queries, using prepared statements, and using stored procedures in SQL Server.
Before getting started with the methods, let us create a product table that can be used as an example of the following methods.
CREATE TABLE Products (
ProductID INT IDENTITY(1,1) PRIMARY KEY,
Name NVARCHAR(100) NOT NULL,
Category NVARCHAR(50) NOT NULL,
Price DECIMAL(10,2) NOT NULL
);
INSERT INTO Products (Name, Category, Price) VALUES
('Laptop', 'Electronics', 1200.00),
('Smartphone', 'Electronics', 800.00),
('Desk Chair', 'Furniture', 150.00),
('Table Lamp', 'Home Decor', 45.00),
('Headphones', 'Electronics', 250.00);
Select * from Products;
This is how the table looks once it is created.
Method 1: Using Parameterized Queries in SQL Server
A parameterized query is an SQL Server query where placeholders (@parameters) are utilized instead of embedding user input directly into the SQL statement. This is to avoid SQL injection by passing input as data, not as executable code.
Syntax:
DECLARE @ParameterName DataType = 'UserInputValue';
EXEC sp_executesql
N'SELECT column_names FROM table_name WHERE column_name = @ParameterName',
N'@ParameterName DataType',
@ParameterName;
Example:
DECLARE @ProductName NVARCHAR(100) = 'Laptop';
EXEC sp_executesql
N'SELECT Price,name FROM Products WHERE Name = @ProductName',
N'@ProductName NVARCHAR(100)',
@ProductName;
Output:
Explanation: Here, the DECLARE @ProductName NVARCHAR(100) syntax is used to declare a variable for user input. The @ProductName variable treats the user input as data and not an SQL query. The WHERE Clause limits returned records to ones with NAME = ‘Laptop’.
Method 2: Using a Stored Procedure in SQL Server
A pre-defined SQL query with parameters can be executed by using a Stored Procedure to prevent SQL injection.
Syntax:
CREATE PROCEDURE ProcedureName
@ParameterName DataType
AS
BEGIN
SELECT column_names FROM table_name WHERE column_name = @ParameterName;
END;
Example:
IF NOT EXISTS (SELECT * FROM sysobjects WHERE name='Products' AND xtype='U')
BEGIN
CREATE TABLE Products (
ProductID INT IDENTITY(1,1) PRIMARY KEY,
Name NVARCHAR(100) NOT NULL,
Category NVARCHAR(50) NOT NULL,
Price DECIMAL(10,2) NOT NULL
);
END
GO
IF NOT EXISTS (SELECT 1 FROM Products)
BEGIN
INSERT INTO Products (Name, Category, Price) VALUES
('Laptop', 'Electronics', 1200.00),
('Smartphone', 'Electronics', 800.00),
('Desk Chair', 'Furniture', 150.00),
('Table Lamp', 'Home Decor', 45.00),
('Headphones', 'Electronics', 250.00);
END
GO
IF OBJECT_ID('GetProductByName', 'P') IS NOT NULL
DROP PROCEDURE GetProductByName;
GO
CREATE PROCEDURE GetProductByName
@ProductName NVARCHAR(100)
AS
BEGIN
SET NOCOUNT ON;
SELECT ProductID,Name FROM Products WHERE Name = @ProductName;
END;
GO
EXEC GetProductByName @ProductName = 'Headphones';
Output:
Explanation: Here, the stored procedure, using a product name as input, GetProductByName, retrieves records from the Products table that match. Using EXEC GetProductByName ‘Laptop’, the records with a laptop as a product are retrieved.
Get 100% Hike!
Master Most in Demand Skills Now!
Method 3: Using User-defined Functions for Filtering in SQL Server
A UDF is a reusable function that accepts input parameters and produces a table or a value.
Syntax:
CREATE FUNCTION FunctionName (@ParameterName DataType)
RETURNS TABLE
AS
RETURN
(
SELECT column_names FROM table_name WHERE column_name = @ParameterName
);
Example:
IF NOT EXISTS (SELECT * FROM sysobjects WHERE name='Products' AND xtype='U')
BEGIN
CREATE TABLE Products (
ProductID INT IDENTITY(1,1) PRIMARY KEY,
Name NVARCHAR(100) NOT NULL,
Category NVARCHAR(50) NOT NULL,
Price DECIMAL(10,2) NOT NULL
);
END
GO
IF NOT EXISTS (SELECT 1 FROM Products)
BEGIN
INSERT INTO Products (Name, Category, Price) VALUES
('Laptop', 'Electronics', 1200.00),
('Smartphone', 'Electronics', 800.00),
('Desk Chair', 'Furniture', 150.00),
('Table Lamp', 'Home Decor', 45.00),
('Headphones', 'Electronics', 250.00);
END
GO
IF OBJECT_ID('dbo.GetProductsByCategory', 'IF') IS NOT NULL
DROP FUNCTION dbo.GetProductsByCategory;
GO
CREATE FUNCTION dbo.GetProductsByCategory (@Category NVARCHAR(50))
RETURNS TABLE
AS
RETURN
(
SELECT * FROM Products WHERE Category = @Category
);
GO
SELECT * FROM dbo.GetProductsByCategory('Electronics');
GO
Output:
Explanation: Here, all products in the ‘Products’ table that belong to a particular category are returned in this case by the User-Defined Function (UDF) GetProductsByCategory. All products in the category “Electronics” are returned by the GetProductsByCategory(‘Electronics’) function.
Method 4: Using Views to Abstract Queries in SQL Server
In SQL Server, a view is a virtual table that holds a pre-written SQL query.
Syntax:
CREATE VIEW ViewName AS
SELECT column_names FROM table_name WHERE condition;
Example:
IF NOT EXISTS (SELECT * FROM sysobjects WHERE name='Products' AND xtype='U')
BEGIN
CREATE TABLE Products (
ProductID INT IDENTITY(1,1) PRIMARY KEY,
Name NVARCHAR(100) NOT NULL,
Category NVARCHAR(50) NOT NULL,
Price DECIMAL(10,2) NOT NULL
);
END
GO
IF NOT EXISTS (SELECT 1 FROM Products)
BEGIN
INSERT INTO Products (Name, Category, Price) VALUES
('Laptop', 'Electronics', 1200.00),
('Smartphone', 'Electronics', 800.00),
('Desk Chair', 'Furniture', 150.00),
('Table Lamp', 'Home Decor', 45.00),
('Headphones', 'Electronics', 250.00);
END
GO
IF OBJECT_ID('dbo.ElectronicsProducts', 'V') IS NOT NULL
DROP VIEW dbo.ElectronicsProducts;
GO
CREATE VIEW dbo.ElectronicsProducts AS
SELECT * FROM Products WHERE Category = 'Electronics';
GO
SELECT * FROM dbo.ElectronicsProducts;
GO
Output:
Explanation: Here, the ElectronicsProducts view contains a predefined query that filters for items in the Electronics category. Hence, the SELECT * FROM dbo.ElectronicsProducts query returns all Electronic products without the need to rewrite the filtering condition.
| Method |
Use Case |
Pros |
Cons |
| Using Parameterized Queries |
Executing dynamic queries requires user input |
It is simple to implement and performs efficiently in addressing SQL injection |
In certain cases, changes in code and complex syntax are required |
| Using a Stored Procedure |
When parameters are used in repetitive queries |
No direct access will be given to the table |
More maintenance is required |
| Using User-defined functions |
When encapsulating reusable logic that produces a table or value |
The reusability of the code is improved |
We have to verify if the input and output data types match |
| Using Views |
Used whenever we have to limit access |
Improves the performance by simplifying the query |
Parameters are not accepted directly |
Best Practices
- Always use parameterized queries: Prevents SQL injection by handling input as data, not as executable SQL query.
- Avoid Dynamic SQL: Do NOT string user input into SQL queries
- Use Parameters: Prevents SQL injection by compelling the use of parameters.
- Check user input before using it: Make sure that only valid data is passed to the database.
Start Your SQL Adventure!
Start Your SQL Journey for Free Today
Conclusion
Although dynamic and interactive applications require SQL queries, they should still be executed carefully to preserve the application’s security and effectiveness. Each of those methods has advantages in managing user input and avoiding risks such as SQL injection
In this blog, you have gained knowledge of different methods of adding user input to an SQL statement.
Take your skills to the next level by enrolling in our SQL Training Course today and gaining hands-on experience. Also, prepare for job interviews with our SQL interview questions, prepared by industry experts.
Q1. What is the safest way to add user input to a SQL statement?
Parameterized queries or stored procedures are the safest way to add user input
Q2. Why should I not directly concatenate user input in SQL queries?
The database may be compromised by SQL injection attacks, which are made possible by direct concatenation in queries.
Q3. How do parameterized queries increase security?
They guarantee that user input is handled as data rather than executable code by separating SQL logic from it.
Q4. Can SQL Server user input be entered into user-defined functions?
Yes, functions that take parameters and return results based on user input can be scalar or table-valued.
Q5. How to prevent SQL injection in Dynamic SQL?
Instead of using simple EXEC with concatenated strings, use sp_executesql with parameterized input.