DELETE with WHERE clause in MySQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to delete rows from the table named 'employees'.

MySQL

DELETE FROM [1];

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

Aemp

Bemployee

Cemployees

Dstaff

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong table name like 'employee' or 'emp'.

Forgetting the table name entirely.

The correct table name is 'employees'. This command deletes all rows from that table.

2fill in blank

medium

Complete the code to delete employees whose department is 'Sales'.

MySQL

DELETE FROM employees WHERE department = '[1]';

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

ASales

BHR

CMarketing

DFinance

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong department name.

Forgetting the quotes around the string value.

The WHERE clause filters rows where the department is 'Sales'. Only those rows are deleted.

3fill in blank

hard

Fix the error in the DELETE statement to remove employees with salary less than 30000.

MySQL

DELETE FROM employees WHERE salary [1] 30000;

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

A>

B<

C=

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' instead of a comparison operator.

Using '>' which deletes employees with salary greater than 30000.

The condition should be 'salary < 30000' to delete employees earning less than 30000.

4fill in blank

hard

Fill both blanks to delete employees who are in department 'HR' and have salary greater than 50000.

MySQL

DELETE FROM employees WHERE department = '[1]' AND salary [2] 50000;

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

AHR

B<

C>

DSales

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the comparison operator.

Using wrong department name.

The condition filters employees in 'HR' with salary greater than 50000.

5fill in blank

hard

Fill all three blanks to delete employees whose name starts with 'J', are in 'Marketing' department, and have salary less than 40000.

MySQL

DELETE FROM employees WHERE name LIKE '[1]' AND department = '[2]' AND salary [3] 40000;

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

AJ%

BMarketing

C<

DSales

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' instead of LIKE for name pattern.

Wrong department or comparison operator.

The LIKE 'J%' matches names starting with 'J'. The department is 'Marketing' and salary less than 40000.

Practice

1. What does the WHERE clause do in a DELETE statement in MySQL?

easy

A. It limits which rows get deleted based on a condition.

B. It specifies the table to delete from.

C. It adds new rows to the table.

D. It changes the structure of the table.

Solution

1. Step 1: Understand the role of DELETE

   The DELETE statement removes rows from a table.

2. Step 2: Understand the role of WHERE

   The WHERE clause filters which rows are affected by DELETE.

3. Final Answer:

   It limits which rows get deleted based on a condition. -> Option A

4. Quick Check:

   WHERE clause = filter rows to delete [OK]

Hint: WHERE filters rows to delete, else all rows removed [OK]

Common Mistakes:

• Thinking WHERE adds rows
• Confusing WHERE with table name
• Assuming DELETE changes table structure

2. Which of the following is the correct syntax to delete rows where the column age is less than 18 from a table named users?

easy

A. DELETE users WHERE age < 18;

B. DELETE FROM users WHERE age < 18;

C. DELETE * FROM users WHERE age < 18;

D. DELETE FROM users IF age < 18;

Solution

1. Step 1: Check DELETE syntax

   The correct syntax starts with DELETE FROM followed by the table name.

2. Step 2: Verify WHERE clause usage

   WHERE clause uses condition like age < 18 to filter rows.

3. Final Answer:

   DELETE FROM users WHERE age < 18; -> Option B

4. Quick Check:

   Correct DELETE syntax = DELETE FROM users WHERE age < 18; [OK]

Hint: Use DELETE FROM table WHERE condition; [OK]

Common Mistakes:

• Omitting FROM keyword
• Using DELETE * which is invalid
• Replacing WHERE with IF

3. Given the table employees with rows:
{id:1, name:'Alice', dept:'HR'},
{id:2, name:'Bob', dept:'IT'},
{id:3, name:'Carol', dept:'HR'}
What will be the remaining rows after running:
DELETE FROM employees WHERE dept = 'HR';

medium

A. [{id:2, name:'Bob', dept:'IT'}]

B. [{id:1, name:'Alice', dept:'HR'}, {id:3, name:'Carol', dept:'HR'}]

C. [] (empty table)

D. [{id:1, name:'Alice', dept:'HR'}, {id:2, name:'Bob', dept:'IT'}, {id:3, name:'Carol', dept:'HR'}]

Solution

1. Step 1: Identify rows matching WHERE condition

   Rows with dept = 'HR' are Alice and Carol (id 1 and 3).

2. Step 2: Delete matching rows and keep others

   Only Bob (id 2) with dept 'IT' remains after deletion.

3. Final Answer:

   [{id:2, name:'Bob', dept:'IT'}] -> Option A

4. Quick Check:

   Deleted HR rows, kept IT row [OK]

Hint: Delete rows matching condition; others stay [OK]

Common Mistakes:

• Deleting all rows by missing WHERE
• Keeping deleted rows by mistake
• Confusing which rows match condition

4. What is wrong with this query?
DELETE FROM orders WHERE;

medium

A. DELETE requires SELECT keyword.

B. DELETE cannot have WHERE clause.

C. Missing condition after WHERE clause.

D. Table name is missing.

Solution

1. Step 1: Check syntax after WHERE

   WHERE clause must have a condition to filter rows.

2. Step 2: Identify missing condition error

   Query ends with WHERE but no condition is given, causing syntax error.

3. Final Answer:

   Missing condition after WHERE clause. -> Option C

4. Quick Check:

   WHERE needs condition [OK]

Hint: Always add condition after WHERE [OK]

Common Mistakes:

• Leaving WHERE empty
• Thinking WHERE is optional but incomplete
• Confusing DELETE syntax with SELECT

5. You have a table products with columns id, name, and stock. You want to delete all products that have zero stock but keep products with NULL stock values. Which query correctly deletes only products with stock exactly zero?

hard

A. DELETE FROM products WHERE stock <= 0;

B. DELETE FROM products WHERE stock IS NULL;

C. DELETE FROM products WHERE stock != NULL;

D. DELETE FROM products WHERE stock = 0;

Solution

1. Step 1: Understand NULL behavior in WHERE

   Comparisons with NULL using =, !=, <= return UNKNOWN (false); use IS NULL to check NULL.

2. Step 2: Identify condition for stock exactly zero

   stock = 0 matches only zero, excludes NULL and other values.

3. Step 3: Analyze other options

   stock <= 0 deletes zero and negatives (keeps NULL); stock IS NULL deletes NULL stocks; stock != NULL never matches (comparison with NULL always UNKNOWN).

4. Final Answer:

   DELETE FROM products WHERE stock = 0; -> Option D

5. Quick Check:

   Use = 0 to delete zero stock only [OK]

Hint: Use = 0 to delete zero, IS NULL for nulls [OK]

Common Mistakes:

• Using <= 0 deletes negatives too
• Using != NULL deletes nothing
• Confusing NULL with zero