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PL/SQL Anti-Patterns Overview

Using SELECT INTO Without Exception Handling

-- Anti-pattern: No exception handling for SELECT INTO
DECLARE
  v_customer_name VARCHAR2(100);
BEGIN
  SELECT customer_name INTO v_customer_name
  FROM customers
  WHERE customer_id = 123;
  
  -- If no rows or multiple rows are found, an exception will be raised
  -- and the rest of the code won't execute
END;

-- Better approach: Use proper exception handling
DECLARE
  v_customer_name VARCHAR2(100);
BEGIN
  SELECT customer_name INTO v_customer_name
  FROM customers
  WHERE customer_id = 123;
  
  -- Process the data
  DBMS_OUTPUT.PUT_LINE('Customer name: ' || v_customer_name);
  
EXCEPTION
  WHEN NO_DATA_FOUND THEN
    DBMS_OUTPUT.PUT_LINE('Customer not found');
  WHEN TOO_MANY_ROWS THEN
    DBMS_OUTPUT.PUT_LINE('Multiple customers found');
  WHEN OTHERS THEN
    DBMS_OUTPUT.PUT_LINE('Error: ' || SQLERRM);
END;

Always include exception handling when using SELECT INTO statements. This helps your code handle situations where no rows or multiple rows are found, preventing unhandled exceptions.

Using Dynamic SQL Unnecessarily

-- Anti-pattern: Using dynamic SQL unnecessarily
DECLARE
  v_sql VARCHAR2(1000);
  v_count NUMBER;
BEGIN
  v_sql := 'SELECT COUNT(*) FROM employees WHERE department_id = 10';
  EXECUTE IMMEDIATE v_sql INTO v_count;
  DBMS_OUTPUT.PUT_LINE('Count: ' || v_count);
END;

-- Better approach: Use static SQL when possible
DECLARE
  v_count NUMBER;
BEGIN
  SELECT COUNT(*) INTO v_count
  FROM employees
  WHERE department_id = 10;
  DBMS_OUTPUT.PUT_LINE('Count: ' || v_count);
END;

Avoid using dynamic SQL (EXECUTE IMMEDIATE) when static SQL would suffice. Dynamic SQL prevents the database from caching execution plans, can introduce security vulnerabilities if not properly parameterized, and makes code harder to read and maintain.

Not Using Bind Variables

-- Anti-pattern: String concatenation in dynamic SQL
DECLARE
  v_dept_id NUMBER := 10;
  v_sql VARCHAR2(1000);
  v_count NUMBER;
BEGIN
  v_sql := 'SELECT COUNT(*) FROM employees WHERE department_id = ' || v_dept_id;
  EXECUTE IMMEDIATE v_sql INTO v_count;
END;

-- Better approach: Use bind variables
DECLARE
  v_dept_id NUMBER := 10;
  v_count NUMBER;
BEGIN
  EXECUTE IMMEDIATE 'SELECT COUNT(*) FROM employees WHERE department_id = :dept_id'
    INTO v_count
    USING v_dept_id;
END;

Always use bind variables (parameter binding) when working with dynamic SQL. This prevents SQL injection attacks, improves performance through plan reuse, and reduces the load on the shared pool.

Using Autonomous Transactions Inappropriately

-- Anti-pattern: Using autonomous transactions unnecessarily
CREATE OR REPLACE PROCEDURE log_action (
  p_action_type VARCHAR2,
  p_description VARCHAR2
) AS
  PRAGMA AUTONOMOUS_TRANSACTION;
BEGIN
  INSERT INTO action_log (action_type, description, log_date)
  VALUES (p_action_type, p_description, SYSDATE);
  COMMIT;
END;

-- Better approach: Consider if autonomous transaction is really needed
CREATE OR REPLACE PROCEDURE process_order (
  p_order_id NUMBER
) AS
BEGIN
  -- Process the order
  UPDATE orders SET status = 'PROCESSED' WHERE order_id = p_order_id;
  
  -- Log the action (without autonomous transaction)
  INSERT INTO action_log (action_type, description, log_date)
  VALUES ('ORDER_PROCESSED', 'Order ' || p_order_id || ' processed', SYSDATE);
  
  -- Single commit for both operations
  COMMIT;
END;

Use autonomous transactions only when necessary, such as for logging errors that should persist even if the main transaction is rolled back. Overusing autonomous transactions can lead to data inconsistency and make debugging more difficult.

Using ROWID Directly

-- Anti-pattern: Using ROWID directly
DECLARE
  v_rowid ROWID;
BEGIN
  SELECT ROWID INTO v_rowid
  FROM employees
  WHERE employee_id = 100;
  
  -- Later in the code or in another session
  UPDATE employees
  SET salary = 5000
  WHERE ROWID = v_rowid;
END;

-- Better approach: Use primary keys or unique constraints
DECLARE
  v_emp_id NUMBER;
BEGIN
  SELECT employee_id INTO v_emp_id
  FROM employees
  WHERE employee_id = 100;
  
  -- Later in the code or in another session
  UPDATE employees
  SET salary = 5000
  WHERE employee_id = v_emp_id;
END;

Avoid using ROWID directly in your code. ROWIDs can change due to operations like export/import or table reorganization. Use primary keys or unique constraints instead for reliable row identification.

Using Implicit Cursors for Bulk Operations

-- Anti-pattern: Row-by-row processing with implicit cursor
DECLARE
  CURSOR c_emp IS
    SELECT employee_id, salary
    FROM employees
    WHERE department_id = 10;
  v_emp_rec c_emp%ROWTYPE;
BEGIN
  OPEN c_emp;
  LOOP
    FETCH c_emp INTO v_emp_rec;
    EXIT WHEN c_emp%NOTFOUND;
    
    UPDATE employee_stats
    SET total_salary = total_salary + v_emp_rec.salary
    WHERE dept_id = 10;
  END LOOP;
  CLOSE c_emp;
END;

-- Better approach: Use BULK COLLECT and FORALL
DECLARE
  TYPE emp_id_tab IS TABLE OF employees.employee_id%TYPE;
  TYPE salary_tab IS TABLE OF employees.salary%TYPE;
  
  v_emp_ids emp_id_tab;
  v_salaries salary_tab;
BEGIN
  SELECT employee_id, salary
  BULK COLLECT INTO v_emp_ids, v_salaries
  FROM employees
  WHERE department_id = 10;
  
  FORALL i IN 1..v_emp_ids.COUNT
    UPDATE employee_stats
    SET total_salary = total_salary + v_salaries(i)
    WHERE dept_id = 10;
END;

Use BULK COLLECT and FORALL for bulk operations instead of row-by-row processing with cursors. Bulk operations significantly reduce context switching between SQL and PL/SQL engines, improving performance for operations on multiple rows.

Not Using Package Variables Appropriately

-- Anti-pattern: Using package variables inappropriately
CREATE OR REPLACE PACKAGE global_data AS
  g_user_id NUMBER;
  g_department_id NUMBER;
  
  PROCEDURE set_context(p_user_id NUMBER, p_dept_id NUMBER);
END global_data;

CREATE OR REPLACE PACKAGE BODY global_data AS
  PROCEDURE set_context(p_user_id NUMBER, p_dept_id NUMBER) IS
  BEGIN
    g_user_id := p_user_id;
    g_department_id := p_dept_id;
  END set_context;
END global_data;

-- Better approach: Use Oracle's built-in context
CREATE OR REPLACE PACKAGE app_context AS
  PROCEDURE set_context(p_user_id NUMBER, p_dept_id NUMBER);
  FUNCTION get_user_id RETURN NUMBER;
  FUNCTION get_department_id RETURN NUMBER;
END app_context;

CREATE OR REPLACE PACKAGE BODY app_context AS
  PROCEDURE set_context(p_user_id NUMBER, p_dept_id NUMBER) IS
  BEGIN
    DBMS_SESSION.SET_CONTEXT('APP_CTX', 'USER_ID', p_user_id);
    DBMS_SESSION.SET_CONTEXT('APP_CTX', 'DEPT_ID', p_dept_id);
  END set_context;
  
  FUNCTION get_user_id RETURN NUMBER IS
  BEGIN
    RETURN TO_NUMBER(SYS_CONTEXT('APP_CTX', 'USER_ID'));
  END get_user_id;
  
  FUNCTION get_department_id RETURN NUMBER IS
  BEGIN
    RETURN TO_NUMBER(SYS_CONTEXT('APP_CTX', 'DEPT_ID'));
  END get_department_id;
END app_context;

Be cautious with package variables. They persist for the duration of a session and can lead to unexpected behavior in multi-user environments. Use Oracle’s built-in context (SYS_CONTEXT) for session-specific information, and consider package state carefully.

Using DBMS_OUTPUT for Production Logging

-- Anti-pattern: Using DBMS_OUTPUT for production logging
CREATE OR REPLACE PROCEDURE process_order(p_order_id NUMBER) AS
BEGIN
  DBMS_OUTPUT.PUT_LINE('Processing order ' || p_order_id);
  
  -- Process the order
  
  DBMS_OUTPUT.PUT_LINE('Order ' || p_order_id || ' processed successfully');
EXCEPTION
  WHEN OTHERS THEN
    DBMS_OUTPUT.PUT_LINE('Error processing order: ' || SQLERRM);
    RAISE;
END;

-- Better approach: Use a proper logging mechanism
CREATE OR REPLACE PROCEDURE process_order(p_order_id NUMBER) AS
BEGIN
  INSERT INTO application_log (log_level, message, log_date)
  VALUES ('INFO', 'Processing order ' || p_order_id, SYSDATE);
  
  -- Process the order
  
  INSERT INTO application_log (log_level, message, log_date)
  VALUES ('INFO', 'Order ' || p_order_id || ' processed successfully', SYSDATE);
  COMMIT;
EXCEPTION
  WHEN OTHERS THEN
    INSERT INTO application_log (log_level, message, log_date)
    VALUES ('ERROR', 'Error processing order: ' || SQLERRM, SYSDATE);
    COMMIT; -- Commit the log entry even if the main transaction is rolled back
    RAISE;
END;

Don’t use DBMS_OUTPUT for production logging. It’s only visible when explicitly enabled by the client and has limited buffer size. Use a proper logging table or Oracle’s built-in logging mechanisms like DBMS_APPLICATION_INFO or DBMS_TRACE.

Not Using Named Notation for Parameters

-- Anti-pattern: Using positional notation for parameters
CREATE OR REPLACE PROCEDURE create_employee(
  p_first_name VARCHAR2,
  p_last_name VARCHAR2,
  p_email VARCHAR2,
  p_phone VARCHAR2,
  p_hire_date DATE,
  p_job_id VARCHAR2,
  p_salary NUMBER,
  p_commission_pct NUMBER,
  p_manager_id NUMBER,
  p_department_id NUMBER
) AS
BEGIN
  -- Procedure body
END;

-- Calling with positional notation
BEGIN
  create_employee('John', 'Doe', 'JDOE', '555-1234', SYSDATE, 'IT_PROG', 5000, NULL, 100, 90);
END;

-- Better approach: Use named notation for parameters
BEGIN
  create_employee(
    p_first_name => 'John',
    p_last_name => 'Doe',
    p_email => 'JDOE',
    p_phone => '555-1234',
    p_hire_date => SYSDATE,
    p_job_id => 'IT_PROG',
    p_salary => 5000,
    p_commission_pct => NULL,
    p_manager_id => 100,
    p_department_id => 90
  );
END;

Use named notation for parameters, especially when calling procedures with many parameters. This improves code readability, makes the code less prone to errors when parameter order changes, and allows you to skip optional parameters.

Not Using %TYPE and %ROWTYPE

-- Anti-pattern: Hardcoding data types
DECLARE
  v_employee_id NUMBER(6);
  v_first_name VARCHAR2(20);
  v_last_name VARCHAR2(25);
  v_email VARCHAR2(25);
  v_phone_number VARCHAR2(20);
  v_hire_date DATE;
BEGIN
  SELECT employee_id, first_name, last_name, email, phone_number, hire_date
  INTO v_employee_id, v_first_name, v_last_name, v_email, v_phone_number, v_hire_date
  FROM employees
  WHERE employee_id = 100;
END;

-- Better approach: Use %TYPE and %ROWTYPE
DECLARE
  v_employee_id employees.employee_id%TYPE;
  v_first_name employees.first_name%TYPE;
  v_last_name employees.last_name%TYPE;
  v_email employees.email%TYPE;
  v_phone_number employees.phone_number%TYPE;
  v_hire_date employees.hire_date%TYPE;
BEGIN
  SELECT employee_id, first_name, last_name, email, phone_number, hire_date
  INTO v_employee_id, v_first_name, v_last_name, v_email, v_phone_number, v_hire_date
  FROM employees
  WHERE employee_id = 100;
END;

-- Even better: Use %ROWTYPE
DECLARE
  v_emp_rec employees%ROWTYPE;
BEGIN
  SELECT *
  INTO v_emp_rec
  FROM employees
  WHERE employee_id = 100;
END;

Use %TYPE and %ROWTYPE to declare variables based on database column and row definitions. This ensures that your variables automatically match the database schema, making your code more maintainable when the schema changes.

Not Using RETURNING Clause

-- Anti-pattern: Separate DML and query
DECLARE
  v_order_id orders.order_id%TYPE := 1001;
  v_new_status orders.status%TYPE := 'SHIPPED';
  v_timestamp orders.last_update_date%TYPE;
BEGIN
  UPDATE orders
  SET status = v_new_status,
      last_update_date = SYSDATE
  WHERE order_id = v_order_id;
  
  -- Separate query to get the timestamp
  SELECT last_update_date
  INTO v_timestamp
  FROM orders
  WHERE order_id = v_order_id;
END;

-- Better approach: Use RETURNING clause
DECLARE
  v_order_id orders.order_id%TYPE := 1001;
  v_new_status orders.status%TYPE := 'SHIPPED';
  v_timestamp orders.last_update_date%TYPE;
BEGIN
  UPDATE orders
  SET status = v_new_status,
      last_update_date = SYSDATE
  WHERE order_id = v_order_id
  RETURNING last_update_date INTO v_timestamp;
END;

Use the RETURNING clause with DML statements (INSERT, UPDATE, DELETE) to retrieve values in a single operation. This improves performance by eliminating the need for a separate query and ensures that you get the exact values that were modified.

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