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SQL Program 33: Departments with no employees

Praveen KulkarniPraveen Kulkarni

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CS TECHIIE | SQL Notes and Solutions

Practical SQL exercise: Finds departments with no matching employee.

Objective

Finds departments with no matching employee.

Explanation

Read the statement clause by clause and predict the result before executing it. These examples use common relational SQL; table setup and exact syntax can vary between MySQL, PostgreSQL, SQL Server, Oracle and SQLite.

Safety check

Before running UPDATE or DELETE, run a SELECT with the same WHERE condition. Use a test database and a transaction for changes you need to verify.

Program / SQL Solution

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

Practice and revision

  • Run the example and verify the output.
  • Change the input and test normal, boundary and invalid cases.
  • Write the solution again without looking at the notes.

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