Why DML operations modify data in MySQL - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to insert a new row into the employees table.

MySQL

INSERT INTO employees (name, age) VALUES ([1], 30);

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

A'John Doe'

BJohn Doe

C"John Doe"

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to use quotes around string values.

Using double quotes instead of single quotes.

The value for a string must be enclosed in single quotes in SQL.

2fill in blank

medium

Complete the code to update the age of an employee named 'Alice'.

MySQL

UPDATE employees SET age = 28 WHERE name = [1];

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

A'Alice'

BAlice

C"Alice"

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Not using quotes around string values in WHERE clause.

Using double quotes instead of single quotes.

String values in SQL conditions must be enclosed in single quotes.

3fill in blank

hard

Fix the error in the DELETE statement to remove employees older than 60.

MySQL

DELETE FROM employees WHERE age [1] 60;

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

A=

B>

C<

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong comparison operator.

Using equals instead of greater than.

To delete employees older than 60, use the greater than operator (>).

4fill in blank

hard

Fill both blanks to select all employees with age {{BLANK_1}} 25 and name {{BLANK_2}} 'Bob'.

MySQL

SELECT * FROM employees WHERE age [1] 25 AND name = [2];

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

A>

B'Bob'

C'Alice'

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operator for age.

Not quoting the name string.

We want employees older than 25 and named 'Bob'. Use > for age and 'Bob' in quotes for name.

5fill in blank

hard

Fill all three blanks to update the salary to {{BLANK_1}} for employee {{BLANK_3}} with id {{BLANK_2}}.

MySQL

UPDATE employees SET salary = [1] WHERE id = [2] AND name = [3];

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

A50000

B101

C'Emma'

D'John'

Attempts:

3 left

💡 Hint

Common Mistakes

Quoting numeric values.

Not quoting string values in WHERE clause.

Set salary to 50000, filter by id 101 and name 'Emma' (quoted).

Practice

1. Which of the following DML commands is used to add new rows to a table in MySQL?

easy

A. UPDATE

B. SELECT

C. DELETE

D. INSERT

Solution

1. Step 1: Understand the purpose of DML commands

   DML commands modify data in tables by adding, changing, or removing rows.

2. Step 2: Identify the command for adding data

   INSERT adds new rows, UPDATE changes existing rows, DELETE removes rows, and SELECT only reads data.

3. Final Answer:

   INSERT -> Option D

4. Quick Check:

   Add new rows = INSERT [OK]

Hint: INSERT adds rows, UPDATE changes, DELETE removes [OK]

Common Mistakes:

• Confusing UPDATE with INSERT
• Thinking SELECT modifies data
• Using DELETE to add data

2. Which of the following is the correct syntax to update a user's email in a table named users?

easy

A. SELECT email = '[e-mail]' FROM users WHERE id = 5;

B. INSERT INTO users SET email = '[e-mail]' WHERE id = 5;

C. UPDATE users SET email = '[e-mail]' WHERE id = 5;

D. DELETE FROM users SET email = '[e-mail]' WHERE id = 5;

Solution

1. Step 1: Recognize the correct DML command for changing data

   To change existing data, UPDATE is used with SET to assign new values.

2. Step 2: Check syntax correctness

   UPDATE users SET email = '[e-mail]' WHERE id = 5; correctly updates the email for user with id 5.

3. Final Answer:

   UPDATE users SET email = '[e-mail]' WHERE id = 5; -> Option C

4. Quick Check:

   Update data uses UPDATE + SET + WHERE [OK]

Hint: UPDATE uses SET and WHERE to change data [OK]

Common Mistakes:

• Using INSERT instead of UPDATE to modify data
• Omitting WHERE clause causing all rows to update
• Using DELETE or SELECT incorrectly

3. Given the table products with columns id, name, and price, what will be the result of this query?

UPDATE products SET price = price * 1.1 WHERE id = 3;

medium

A. The price of the product with id 3 will increase by 10%.

B. All product prices will increase by 10%.

C. The product with id 3 will be deleted.

D. Syntax error due to missing WHERE clause.

Solution

1. Step 1: Understand the UPDATE statement with WHERE clause

   The query updates only rows where id = 3, so only that product is affected.

2. Step 2: Analyze the price update expression

   The price is multiplied by 1.1, increasing it by 10% for the product with id 3.

3. Final Answer:

   The price of the product with id 3 will increase by 10%. -> Option A

4. Quick Check:

   UPDATE with WHERE affects specific rows [OK]

Hint: WHERE limits UPDATE to specific rows [OK]

Common Mistakes:

• Assuming all rows update without WHERE
• Confusing UPDATE with DELETE
• Thinking syntax error occurs without WHERE

4. Identify the error in this DELETE statement:

DELETE users WHERE id = 10;

medium

A. Missing FROM keyword after DELETE.

B. WHERE clause cannot be used with DELETE.

C. DELETE cannot remove rows based on conditions.

D. Table name should be in quotes.

Solution

1. Step 1: Recall correct DELETE syntax

   The correct syntax is DELETE FROM table_name WHERE condition;. The FROM keyword is required.

2. Step 2: Identify the missing keyword

   The statement misses FROM after DELETE, causing a syntax error.

3. Final Answer:

   Missing FROM keyword after DELETE. -> Option A

4. Quick Check:

   DELETE requires FROM before table name [OK]

Hint: DELETE syntax: DELETE FROM table WHERE condition [OK]

Common Mistakes:

• Omitting FROM keyword
• Using DELETE without WHERE to remove specific rows
• Quoting table names unnecessarily

5. You want to increase the salary by 5% for all employees in the employees table who work in the 'Sales' department. Which query correctly performs this update?

hard

A. DELETE FROM employees WHERE department = 'Sales';

B. UPDATE employees SET salary = salary * 1.05 WHERE department = 'Sales';

C. INSERT INTO employees SET salary = salary * 1.05 WHERE department = 'Sales';

D. UPDATE employees WHERE department = 'Sales' SET salary = salary * 1.05;

Solution

1. Step 1: Choose the correct DML command for modifying existing data

   To change salaries, UPDATE is used, not INSERT or DELETE.

2. Step 2: Verify correct syntax order

   The correct syntax is UPDATE table SET column = value WHERE condition;. UPDATE employees SET salary = salary * 1.05 WHERE department = 'Sales'; follows this order correctly.

3. Final Answer:

   UPDATE employees SET salary = salary * 1.05 WHERE department = 'Sales'; -> Option B

4. Quick Check:

   UPDATE + SET + WHERE with correct order [OK]

Hint: UPDATE SET comes before WHERE clause [OK]

Common Mistakes:

• Using INSERT to modify data
• Placing WHERE before SET in UPDATE
• Deleting rows instead of updating