Join order and performance impact in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all columns from the two tables joined on the customer ID.

SQL

SELECT * FROM customers [1] orders ON customers.customer_id = orders.customer_id;

Drag options to blanks, or click blank then click option'

AJOIN

BWHERE

CGROUP BY

DORDER BY

Attempts:

3 left

💡 Hint

Common Mistakes

Using WHERE instead of JOIN to combine tables.

Using GROUP BY or ORDER BY which are for grouping or sorting, not joining.

The JOIN keyword is used to combine rows from two or more tables based on a related column.

2fill in blank

medium

Complete the code to perform an inner join between products and sales on product_id.

SQL

SELECT products.name, sales.quantity FROM products [1] JOIN sales ON products.product_id = sales.product_id;

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ALEFT

BRIGHT

CFULL

DINNER

Attempts:

3 left

💡 Hint

Common Mistakes

Using LEFT or RIGHT join which include unmatched rows from one table.

Using FULL join which includes unmatched rows from both tables.

An INNER JOIN returns only the rows where there is a match in both tables.

3fill in blank

hard

Fix the error in the join condition to correctly join employees and departments on department_id.

SQL

SELECT employees.name, departments.name FROM employees JOIN departments ON employees.[1] = departments.department_id;

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Adept_id

Bdepartment

Cdepartment_id

Ddept

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong or incomplete column name in the join condition.

Using a column that does not exist in the employees table.

The join condition must use the exact column name department_id from employees to match departments.

4fill in blank

hard

Fill both blanks to write a query that joins orders and customers, selecting order_id and customer name, filtering only orders with amount greater than 100.

SQL

SELECT orders.order_id, customers.name FROM orders [1] JOIN customers ON orders.customer_id = customers.customer_id WHERE orders.amount [2] 100;

Drag options to blanks, or click blank then click option'

AINNER

B>

C<

DLEFT

Attempts:

3 left

💡 Hint

Common Mistakes

Using LEFT join which includes unmatched rows.

Using < instead of > in the WHERE clause.

Use INNER JOIN to get matching rows and > to filter amounts greater than 100.

5fill in blank

hard

Fill all three blanks to write a query that joins three tables: sales, products, and categories. Select product name and category name for sales with quantity less than 50.

SQL

SELECT products.name, categories.name FROM sales [1] JOIN products ON sales.product_id = products.product_id [2] JOIN categories ON products.category_id = categories.category_id WHERE sales.quantity [3] 50;

Drag options to blanks, or click blank then click option'

AINNER

B<

DLEFT

Attempts:

3 left

💡 Hint

Common Mistakes

Using LEFT join which includes unmatched rows.

Using > instead of < in the WHERE clause.

Use INNER JOIN for both joins to get matching rows only, and < to filter quantity less than 50.