Finding duplicates efficiently in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select duplicate names from the users table.

SQL

SELECT name, COUNT(*) FROM users GROUP BY [1] HAVING COUNT(*) > 1;

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

Aemail

Bid

Cname

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Grouping by a unique column like id will never find duplicates.

Forgetting to use HAVING COUNT(*) > 1 to filter duplicates.

We group by the name column to find duplicates of names.

2fill in blank

medium

Complete the code to find duplicate emails in the customers table.

SQL

SELECT email, COUNT(*) FROM customers GROUP BY [1] HAVING COUNT(*) > 1;

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

Aemail

Bcustomer_id

Cphone

Daddress

Attempts:

3 left

💡 Hint

Common Mistakes

Grouping by a unique identifier like customer_id will not find duplicates.

Not using HAVING clause to filter groups with more than one row.

Grouping by email helps find duplicate email addresses.

3fill in blank

hard

Fix the error in the code to find duplicate product codes in the inventory table.

SQL

SELECT product_code, COUNT(*) FROM inventory GROUP BY [1] HAVING COUNT(*) > 1;

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

Aproduct_id

Bquantity

Cprice

Dproduct_code

Attempts:

3 left

💡 Hint

Common Mistakes

Grouping by product_id instead of product_code.

Not using HAVING COUNT(*) > 1 to filter duplicates.

The GROUP BY must be on product_code to find duplicates of product codes.

4fill in blank

hard

Fill both blanks to find duplicate usernames and count them in the accounts table.

SQL

SELECT [1], COUNT(*) FROM accounts GROUP BY [2] HAVING COUNT(*) > 1;

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

Ausername

Buser_id

Demail

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting username but grouping by user_id or email.

Grouping by a unique column will not find duplicates.

We select and group by username to find duplicates of usernames.

5fill in blank

hard

Fill all three blanks to find duplicate order numbers and their counts in the orders table.

SQL

SELECT [1], COUNT(*) FROM orders GROUP BY [2] HAVING COUNT(*) [3] 1;

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

Aorder_number

B>

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using HAVING COUNT(*) = 1 which finds unique values, not duplicates.

Grouping by a different column than selected.

We select and group by order_number and filter groups having count greater than 1 to find duplicates.