SQL LEFT JOIN

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LEFT JOIN returns all rows from the left table, and matched rows from the right. If there’s no match, right-side columns return NULL.

🔹 Basic Syntax

SELECT columns
FROM table1
LEFT JOIN table2
  ON table1.common_column = table2.common_column;

🔹 Example: List All Employees with Their Departments

SELECT
  e.employee_name,
  d.department_name
FROM employees e
LEFT JOIN departments d
  ON e.department_id = d.department_id;

✅ Employees with no department still appear, but department_name will be NULL.

🔹 Use Case: Identify Unlinked Records

SELECT e.name
FROM employees e
LEFT JOIN departments d
  ON e.department_id = d.id
WHERE d.id IS NULL;

🟡 This finds employees not assigned to any department.

🧠 Quick Recap

🧩 Use LEFT JOIN when the relationship is optional