Review Execution Plan for Table Joins

Analyzing Join Performance with EXPLAIN

Write a PostgreSQL query to analyze a join between two tables using EXPLAIN, to understand how the join is executed.

Solution:

-- Specify the action to display the execution plan for the query.
EXPLAIN  
-- Define the columns to be selected in the query.
SELECT e.name, d.department_name  
-- Specify the primary table (Employees) and alias it as 'e'.
FROM Employees e  
-- Perform a join with the Departments table, aliasing it as 'd'.
JOIN Departments d 
-- Define the join condition between Employees and Departments.
ON e.department_id = d.department_id;

Explanation:

• Purpose of the Query:
• To inspect how PostgreSQL performs a join operation between two related tables.
• This exercise helps in understanding join strategies such as Nested Loop or Hash Join.
• Key Components:
• JOIN Departments d ON e.department_id = d.department_id : Specifies the join condition.
• EXPLAIN : Outputs the query plan without executing the join.
• Real-World Application:
• Useful for optimizing queries that involve table joins, ensuring that indexes are used efficiently.

Notes:

• Analyze the output to determine if the join method is optimal for the data distribution.

For more Practice: Solve these Related Problems:

• Write a PostgreSQL query using EXPLAIN to analyze an INNER JOIN between "Orders" and "Customers" on customer_id.
• Write a PostgreSQL query using EXPLAIN to analyze a LEFT JOIN between "Employees" and "Salaries" on employee_id.
• Write a PostgreSQL query using EXPLAIN to display the execution plan for a FULL OUTER JOIN between "Products" and "Suppliers".
• Write a PostgreSQL query using EXPLAIN to analyze a multi-table join involving "Orders", "OrderDetails", and "Products".

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