UPDATE with WHERE clause in MySQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to update the salary of employees in the 'employees' table.

MySQL

UPDATE employees SET salary = 5000 WHERE id = [1];

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

Aemployee_id

Bsalary

C10

D'10'

Attempts:

3 left

💡 Hint

Common Mistakes

Putting quotes around numeric IDs causes errors.

Using wrong column names in WHERE clause.

The WHERE clause specifies which rows to update. Here, id = 10 targets the employee with ID 10.

2fill in blank

medium

Complete the code to update the 'status' to 'active' for users with last login before 2023-01-01.

MySQL

UPDATE users SET status = 'active' WHERE last_login < [1];

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

A'2023-01-01'

B2023-01-01

C'01-01-2023'

D2023/01/01

Attempts:

3 left

💡 Hint

Common Mistakes

Not using quotes around the date.

Using wrong date format.

Dates in SQL must be in quotes and in the format 'YYYY-MM-DD'.

3fill in blank

hard

Fix the error in the UPDATE statement to change the 'price' to 19.99 for product with id 5.

MySQL

UPDATE products SET price = [1] WHERE id = 5;

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

A'19.99'

Bprice

C19,99

D19.99

Attempts:

3 left

💡 Hint

Common Mistakes

Putting numeric values in quotes.

Using comma instead of dot for decimals.

Numeric values like prices should not be in quotes in SQL.

4fill in blank

hard

Fill both blanks to update the 'quantity' to 100 for items where 'category' is 'books'.

MySQL

UPDATE inventory SET [1] = 100 WHERE [2] = 'books';

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

Aquantity

Bcategory

Cprice

Dstock

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up column names in SET and WHERE clauses.

Using wrong column names that don't exist.

The quantity column is updated, and the WHERE clause filters rows where category equals 'books'.

5fill in blank

hard

Fill all three blanks to update the 'status' to 'inactive' for users with 'last_login' before '2022-12-31' and 'role' equals 'guest'.

MySQL

UPDATE users SET [1] = 'inactive' WHERE [2] < [3] AND role = 'guest';

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

Astatus

Blast_login

C'2022-12-31'

Dusername

Attempts:

3 left

💡 Hint

Common Mistakes

Not quoting the date string.

Using wrong column names in SET or WHERE.

The status column is updated. The WHERE clause filters users with last_login before the date '2022-12-31' and role 'guest'.

Practice

1. What does the WHERE clause do in an UPDATE statement in MySQL?

easy

A. It specifies which rows should be updated.

B. It creates a new table.

C. It deletes rows from the table.

D. It selects rows to display.

Solution

1. Step 1: Understand the purpose of UPDATE

   The UPDATE command changes data in existing rows of a table.

2. Step 2: Role of WHERE clause

   The WHERE clause limits which rows get changed. Without it, all rows update.

3. Final Answer:

   It specifies which rows should be updated. -> Option A

4. Quick Check:

   WHERE limits rows to update [OK]

Hint: WHERE filters rows to update; no WHERE updates all [OK]

Common Mistakes:

• Thinking WHERE creates or deletes rows
• Confusing UPDATE with SELECT
• Ignoring WHERE causes all rows to update

2. Which of the following is the correct syntax to update the salary to 5000 for employees with id 10 in MySQL?

easy

A. UPDATE employees SET salary = 5000 AND id = 10;

B. UPDATE employees SET salary = 5000 WHERE id = 10;

C. UPDATE employees SET salary WHERE id = 10 = 5000;

D. UPDATE employees WHERE id = 10 SET salary = 5000;

Solution

1. Step 1: Identify correct UPDATE syntax

   The correct order is: UPDATE table SET column = value WHERE condition.

2. Step 2: Check each option

   UPDATE employees SET salary = 5000 WHERE id = 10; follows correct syntax. Others have misplaced clauses or wrong operators.

3. Final Answer:

   UPDATE employees SET salary = 5000 WHERE id = 10; -> Option B

4. Quick Check:

   UPDATE SET column=value WHERE condition [OK]

Hint: SET comes before WHERE in UPDATE statements [OK]

Common Mistakes:

• Placing WHERE before SET
• Using AND instead of WHERE
• Incorrect assignment syntax

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

UPDATE products SET price = price + 10 WHERE id = 3;

Assume the original price for id = 3 was 50.

medium

A. 10

B. 50

C. 60

D. NULL

Solution

1. Step 1: Understand the UPDATE operation

   The query adds 10 to the current price for the product where id = 3.

2. Step 2: Calculate new price

   Original price is 50, so 50 + 10 = 60.

3. Final Answer:

   60 -> Option C

4. Quick Check:

   50 + 10 = 60 [OK]

Hint: Add to existing value only for rows matching WHERE [OK]

Common Mistakes:

• Ignoring WHERE and updating all rows
• Setting price to 10 instead of adding
• Confusing original and updated values

4. Identify the error in this MySQL query:

UPDATE users SET age = 30 WHERE;

medium

A. SET keyword is misplaced.

B. Table name is missing.

C. UPDATE keyword is misspelled.

D. Missing condition after WHERE clause.

Solution

1. Step 1: Analyze the query structure

   The query has UPDATE, SET, and WHERE keywords but WHERE has no condition.

2. Step 2: Identify the error

   WHERE must be followed by a condition to specify which rows to update.

3. Final Answer:

   Missing condition after WHERE clause. -> Option D

4. Quick Check:

   WHERE requires condition [OK]

Hint: WHERE must always have a condition [OK]

Common Mistakes:

• Leaving WHERE empty
• Misplacing SET and WHERE
• Forgetting semicolon

5. You have a table orders with columns order_id, status, and amount. You want to increase the amount by 20% only for orders with status 'pending' and amount less than 100. Which query correctly does this?

hard

A. UPDATE orders SET amount = amount * 1.2 WHERE status = 'pending' AND amount < 100;

B. UPDATE orders SET amount = amount + 20 WHERE status = 'pending' OR amount < 100;

C. UPDATE orders SET amount = amount * 1.2 WHERE status = 'pending' OR amount < 100;

D. UPDATE orders SET amount = amount * 0.2 WHERE status = 'pending' AND amount < 100;

Solution

1. Step 1: Understand the condition

   We want to update only rows where status is 'pending' AND amount is less than 100.

2. Step 2: Calculate new amount

   Increase by 20% means multiply amount by 1.2.

3. Step 3: Check options

   UPDATE orders SET amount = amount * 1.2 WHERE status = 'pending' AND amount < 100; correctly uses AND and multiplies amount by 1.2. Others use OR or wrong calculations.

4. Final Answer:

   UPDATE orders SET amount = amount * 1.2 WHERE status = 'pending' AND amount < 100; -> Option A

5. Quick Check:

   AND condition + *1.2 [OK]

Hint: Use AND for multiple conditions in WHERE [OK]

Common Mistakes:

• Using OR instead of AND
• Adding fixed 20 instead of 20%
• Multiplying by 0.2 instead of 1.2