SQL Server Interview Question #120

How do parameterized queries help prevent SQL injection?

Views, Stored Procedures & User-Defined Functions Mid-Level Intermediate

Detailed Explanation

Parameterized queries keep SQL command structure separate from data values. User input is sent as a typed parameter rather than concatenated into executable SQL text, preventing the value from being interpreted as part of the SQL syntax.

ASP.NET Core applications should use EF Core parameterization, ADO.NET SqlParameter, Dapper parameters, or parameterized stored procedures rather than concatenating untrusted input into SQL strings.

Parameterization is a central SQL injection defense, although dynamic identifiers and intentionally dynamic query structure still require strict validation and safe construction.

Code Example

-- Unsafe pattern:
-- SET @Sql = N'SELECT * FROM Users WHERE Email = ''' + @Email + N'''';

-- Safe parameterized dynamic SQL:
DECLARE @Sql NVARCHAR(MAX) =
    N'SELECT Id, Email
      FROM dbo.Users
      WHERE Email = @Email;';

EXEC sys.sp_executesql
    @Sql,
    N'@Email NVARCHAR(256)',
    @Email = @UserEmail;