Dynamic SQL: FAQs and Best Practices for Generating SQL Queries
1.What is Dynamic SQL and when is it used?
Dynamic SQL in Oracle is SQL statements that are built and executed at runtime by using constructs like EXECUTE IMMEDIATE. It is primarily used for tasks where the query depends on runtime conditions, like dynamic table or column selection.
Example (Oracle)
BEGIN
EXECUTE IMMEDIATE 'SELECT * FROM employees WHERE department_id = 101';
•Creating dynamic WHERE clauses.
•Using runtime determined table or column names.
•Executing database administration tasks automatically.
2.What are the benefits of using Dynamic SQL in Oracle?
Dynamic SQL can be very helpful when building queries that will need to be flexible based on runtime conditions. Some benefits are:
•Dynamic table or column names
•Reduce complexity in conditional logic for a query
•Can do things not possible with static SQL such as DDL:
CREATE TABLE
EXECUTE IMMEDIATE 'CREATE TABLE temp_table (id NUMBER, name VARCHAR2(50))';
END;
This feature helps automate database tasks and manage complex requirements.
3.How is Dynamic SQL implemented in Oracle?
Oracle uses EXECUTE IMMEDIATE for single-statement execution and DBMS_SQL for more complex scenarios, like processing multiple statements.
Example with EXECUTE IMMEDIATE:
DECLARE
v_query VARCHAR2(200);
BEGIN
v_query := 'UPDATE employees SET salary = salary * 1.10 WHERE department_id = :dept_id';
EXECUTE IMMEDIATE v_query USING 101;
END;
Here, :dept_id is a bind variable passed to the dynamic SQL statement.
4.How do you prevent SQL injection in Oracle's Dynamic SQL?
To prevent SQL injection, use bind variables with EXECUTE IMMEDIATE. Avoid concatenating user inputs directly into SQL strings.
Safe Example:
DECLARE
v_query VARCHAR2(200);
BEGIN
v_query := 'SELECT * FROM employees WHERE name = :name';
EXECUTE IMMEDIATE v_query USING 'John';
END;
This method also ensures user inputs are sanitized and eliminates injection vulnerabilities.
5.What are the limitations of Dynamic SQL in Oracle?
Dynamic SQL has limitations like:
•Increased complexity and harder debugging.
•Performance can be affected because execution plan is not reused.
•Explicit handling of permissions for the accessed objects is required.
Example Limitation: Dynamic SQL cannot use bind variables for certain DDL operations:
BEGIN
EXECUTE IMMEDIATE 'CREATE TABLE ' || :table_name || ' (id NUMBER)';
END;
Oracle requires concatenation for object names, which can complicate code.
