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Dynamic SQL

Dynamic SQL is a method of writing SQL statements that are built and executed at runtime. It is useful for creating flexible queries where the structure or criteria depend on variables or user inputs. However, it should be used carefully to avoid security risks like SQL injection.

Using Dynamic SQL

Use the EXEC or sp_executesql system stored procedure to execute dynamic SQL statements.

Example: Using EXEC to Execute Dynamic SQL

DECLARE @TableName NVARCHAR(50) = 'FreedomFighters';
DECLARE @SQLQuery NVARCHAR(1000);

SET @SQLQuery = 'SELECT * FROM ' + @TableName;
EXEC(@SQLQuery);

Explanation: This code constructs a dynamic SQL query to select all records from the FreedomFighters table and executes it using EXEC.

Using sp_executesql for Parameterized Queries

Using sp_executesql allows you to create parameterized dynamic SQL queries, which are safer and more efficient.

Example: Using sp_executesql

DECLARE @SQLQuery NVARCHAR(1000);
DECLARE @City NVARCHAR(50) = 'Chennai';

SET @SQLQuery = 'SELECT * FROM FreedomFighters WHERE City = @City';
EXEC sp_executesql @SQLQuery, N'@City NVARCHAR(50)', @City = @City;

Explanation: This example uses sp_executesql to execute a parameterized query that selects all freedom fighters from the city of Chennai. Using parameters helps prevent SQL injection.

Advantages of Using Dynamic SQL

  • Provides flexibility for building queries based on runtime conditions.
  • Useful for scenarios where table or column names are determined dynamically.
  • Allows the execution of administrative tasks that require dynamic query structures.

Security Concerns

Dynamic SQL can be vulnerable to SQL injection attacks if user input is not properly sanitized. Always use parameterized queries with sp_executesql to mitigate this risk.

Do's and Don'ts

Do's

  • Use sp_executesql with parameters to protect against SQL injection.
  • Validate and sanitize user inputs before using them in dynamic SQL queries.
  • Document dynamic SQL queries for easier maintenance and debugging.

Don'ts

  • Don't use dynamic SQL when static SQL can achieve the same result.
  • Don't concatenate user inputs directly into dynamic SQL queries without validation.
  • Don't forget to test the performance of dynamic SQL queries, as they may be less efficient than static queries.
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