How Can I Securely Parameterize SQL Queries with Dynamic Table Names?

Parameterized SQL queries using dynamic table names

Introduction

In SQL programming, passing variable table names into stored procedures is a common challenge. This article explores the limitations of parameterized queries and provides a reliable solution that is both safe and flexible.

Question

Traditionally, SQL statements are constructed on the client side and passed to the database as strings. This approach is vulnerable to SQL injection attacks as user input can be manipulated to execute malicious commands.

Parameterized query

To mitigate the risk of SQL injection, parameterized queries are introduced. These queries use placeholders in place of user input and then bind the actual values ​​when executed. This prevents malicious code from being injected into the query.

However, there are challenges with parameterized queries when table names are variables. Dynamic SQL (generating query text at runtime) is often used to solve this problem. However, this approach can result in complex and error-prone code.

Secure and flexible solution

A safer and more elegant solution is to use stored procedures with dynamic SQL. The stored procedure takes user input as a parameter and uses it to look up the actual table name from a secure source (such as a database table or XML file).

The following example illustrates this approach:

CREATE PROC spCountAnyTableRows( @PassedTableName AS NVarchar(255) ) AS
-- 安全地计算任何非系统表的行数
BEGIN
    DECLARE @ActualTableName AS NVarchar(255)

    SELECT @ActualTableName = QUOTENAME( TABLE_NAME )
    FROM INFORMATION_SCHEMA.TABLES
    WHERE TABLE_NAME = @PassedTableName

    DECLARE @sql AS NVARCHAR(MAX)
    SELECT @sql = 'SELECT COUNT(*) FROM ' + @ActualTableName + ';'

    EXEC(@SQL)
END

This stored procedure takes the passed table name, looks up the actual table name from the metadata table INFORMATION_SCHEMA.TABLES, and then executes a dynamic SQL query to count the number of rows in the actual table.

Safety Precautions

Using this approach provides several security advantages:

• SQL injection protection: The table name passed is only used for lookups and is not used directly in the executed query.
• Principle of Least Privilege: Limit lookup queries to specific metadata tables or XML files, limiting the potential damage of malicious attacks.

Other notes

• A similar method (INFORMATION_SCHEMA.COLUMNS) can be used to handle dynamic column names.
• Parameterized SQL queries can also be used with dynamic table names, but stored procedures provide a more manageable and secure solution.
• Refactoring table names into a single table with a "name" column is not possible in all cases.

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