SQL DELETE

The DELETE statement is used to remove one or more rows from a table.

🔹 Basic Syntax

DELETE FROM table_name
WHERE condition;

⚠️ Always use a WHERE clause to avoid deleting everything!

🔹 Examples

-- Delete a specific employee
DELETE FROM employees
WHERE employee_id = 101;

-- Delete all employees from the IT department
DELETE FROM employees
WHERE department = 'IT';

🔹 Delete All Rows (Be Cautious!)

-- Delete all rows (but keep the table)
DELETE FROM employees;

-- Oracle tip: Use TRUNCATE for faster delete (no WHERE allowed)
TRUNCATE TABLE employees;

🔹 With Subqueries

-- Delete employees who are not assigned to any department
DELETE FROM employees
WHERE department_id NOT IN (
  SELECT id FROM departments
);

🧠 Quick Recap

Action	Syntax Example
Delete with condition	`DELETE FROM table WHERE ...`
Delete all rows	`DELETE FROM table;`
Fast delete (Oracle)	`TRUNCATE TABLE table_name;`
Delete using subquery	`DELETE WHERE col IN (SELECT ...)`

✅ Use DELETE to clean up data—carefully!