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SQL Program 44: Customers with more than three orders

Praveen KulkarniPraveen Kulkarni

SQL learning illustration

CS TECHIIE | SQL Notes and Solutions

Practical SQL exercise: Filters customers by order count.

Objective

Filters customers by order count.

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 customer_id,COUNT(*) AS order_count FROM orders GROUP BY customer_id HAVING COUNT(*)>3;

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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