Dynamic SQL

Dynamic SQL is a programming technique that allows you to construct SQL statements dynamically at runtime. This means that the full text of the SQL statement is not known until the code is executed. This can be useful for a variety of reasons, such as:

Benefits of Dynamic SQL

Adaptability: Dynamic SQL caters to situations where SQL statements need to be customized based on runtime parameters, user inputs, or changing data. This adaptability is particularly useful in applications that require dynamic filtering, data manipulation, and cross-database queries.

Flexible Data Manipulation: Dynamic SQL enables the creation of complex SQL statements, including INSERT, UPDATE, and DELETE queries, that can vary based on specific requirements. This flexibility is crucial for handling diverse data manipulation tasks and adapting to changing data conditions.

User-Driven Interactions: Dynamic SQL plays a vital role in building applications that respond to user interactions. It allows developers to construct SQL statements based on user input, such as selecting specific records or filtering data based on user-defined criteria.

Security Enhancements: Dynamic SQL can be leveraged to enhance data security by incorporating prepared statements. Prepared statements bind SQL variables to placeholders, reducing the risk of SQL injection attacks.

There are two main ways to use dynamic SQL

Using prepared statements: Prepared statements are a type of dynamic SQL statement that is precompiled by the database server. This can improve performance, as the database server does not need to compile the statement each time it is executed.

Using native dynamic SQL: Native dynamic SQL is a type of dynamic SQL statement that is executed directly by the database engine. This can be less efficient than using prepared statements, but it can be more flexible.


Basic Dynamic SQL Execution

This example shows how to execute a simple SELECT statement using Dynamic SQL.

SET @SQLQuery = 'SELECT * FROM Employees WHERE EmployeeID = 1';
EXECUTE sp_executesql @SQLQuery;

Using Parameters with Dynamic SQL

This example demonstrates how to pass parameters to a Dynamic SQL query.

DECLARE @EmployeeID INT = 1;
SET @SQLQuery = 'SELECT * FROM Employees WHERE EmployeeID = @EmpID';
EXECUTE sp_executesql @SQLQuery, N'@EmpID INT', @EmpID = @EmployeeID;

Building a Dynamic SQL Query with Variable Conditions

This example shows how to construct a more complex SQL statement dynamically based on variable conditions.

DECLARE @Department VARCHAR(50) = 'Sales';
DECLARE @DateFrom DATETIME = '2023-01-01';
DECLARE @DateTo DATETIME = '2023-12-31';

SET @SQLQuery = 'SELECT * FROM Employees WHERE Department = ''' + @Department + ''' 
                AND HireDate BETWEEN ''' + CONVERT(VARCHAR, @DateFrom, 120) + ''' 
                AND ''' + CONVERT(VARCHAR, @DateTo, 120) + '''';


Dynamic SQL for Table Creation

This example shows how to use Dynamic SQL for creating a new table.

DECLARE @TableName NVARCHAR(128) = 'NewTable';

SET @SQLQuery = 'CREATE TABLE ' + @TableName + 
               '(ID INT PRIMARY KEY, Name NVARCHAR(100))';

EXECUTE sp_executesql @SQLQuery;

Dynamic SQL with IF-ELSE Logic

This example illustrates the use of IF-ELSE logic in constructing Dynamic SQL.

DECLARE @IncludeSalary BIT = 1;

IF @IncludeSalary = 1
    SET @SQLQuery = 'SELECT ID, Name, Salary FROM Employees';
    SET @SQLQuery = 'SELECT ID, Name FROM Employees';


Dynamic SQL is often used within stored procedures, functions, or triggers when you need to create custom queries based on runtime conditions. This can be beneficial when dealing with complex logic or optional search criteria.

Dynamic SQL can be a powerful tool for developing database applications. However, it is important to use it safely and responsibly to avoid security vulnerabilities.