UPDATE with WHERE condition in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

SQL

UPDATE employees SET salary = 50000 WHERE id = [1];

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

A'10'

B10

Csalary

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Putting quotes around numeric IDs.

Using column names instead of values in WHERE.

The WHERE clause requires the employee's id as a number, so 10 is correct.

2fill in blank

medium

Complete the code to update the status of orders where the order date is before 2023-01-01.

SQL

UPDATE orders SET status = 'shipped' WHERE order_date [1] '2023-01-01';

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

A>

B=

C<

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using > instead of < for dates before a certain day.

Using = which only matches exact dates.

We want to update orders before 2023-01-01, so the operator should be <.

3fill in blank

hard

Fix the error in the code to update the quantity of products where the product name is 'Widget'.

SQL

UPDATE products SET quantity = 100 WHERE product_name = [1];

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

A'Widget'

BWidget

C"Widget"

Dproduct_name

Attempts:

3 left

💡 Hint

Common Mistakes

Not using quotes around string values.

Using double quotes which may not work in all SQL dialects.

String values in SQL must be enclosed in single quotes, so 'Widget' is correct.

4fill in blank

hard

Fill both blanks to update the price of items where the category is 'Books'.

SQL

UPDATE items SET price = [1] WHERE category = [2];

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

A19.99

B'Books'

CBooks

Dprice

Attempts:

3 left

💡 Hint

Common Mistakes

Putting quotes around numbers.

Not putting quotes around string values.

The price is a number, so 19.99 is correct. The category is a string, so it needs single quotes: 'Books'.

5fill in blank

hard

Fill all three blanks to update the 'status' to 'active' for users with age greater than 30.

SQL

UPDATE users SET [1] = [2] WHERE [3] > 30;

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

Astatus

B'active'

Cage

Dusername

Attempts:

3 left

💡 Hint

Common Mistakes

Using column names instead of values.

Not quoting string values.

Using wrong column in WHERE clause.

We update the status column to the string 'active' for users whose age is greater than 30.

Practice

1.

What does the WHERE clause do in an UPDATE statement?

easy

A. It adds new rows to the table.

B. It changes the table structure.

C. It limits which rows get updated.

D. It deletes rows from the table.

Solution

1. Step 1: Understand the purpose of UPDATE

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

2. Step 2: Role of WHERE clause in UPDATE

   The WHERE clause specifies which rows should be changed, so only those rows are updated.

3. Final Answer:

   It limits which rows get updated. -> Option C

4. Quick Check:

   WHERE clause = row filter [OK]

Hint: WHERE filters rows to update only those needed [OK]

Common Mistakes:

• Thinking WHERE adds or deletes rows
• Believing UPDATE changes table structure
• Ignoring WHERE updates all rows

2.

Which of the following is the correct syntax to update the salary to 5000 for employees with id 3?

UPDATE employees SET salary = 5000 WHERE id = 3;

easy

A. UPDATE employees SET salary 5000 WHERE id = 3;

B. UPDATE employees salary = 5000 WHERE id = 3;

C. UPDATE employees SET salary = 5000 id = 3;

D. UPDATE employees SET salary = 5000 WHERE id = 3;

Solution

1. Step 1: Check UPDATE syntax

   The correct syntax requires SET before column assignment and WHERE for condition.

2. Step 2: Validate each option

   UPDATE employees SET salary = 5000 WHERE id = 3; uses SET and WHERE correctly; others miss SET or WHERE or have wrong syntax.

3. Final Answer:

   UPDATE employees SET salary = 5000 WHERE id = 3; -> Option D

4. Quick Check:

   SET + WHERE = correct UPDATE syntax [OK]

Hint: Always use SET before column assignments in UPDATE [OK]

Common Mistakes:

• Omitting SET keyword
• Forgetting WHERE clause
• Missing equal sign (=) in assignment

3.

Given the table products:

id | name    | price
---+---------+-------
1  | Pen     | 10
2  | Pencil  | 5
3  | Eraser  | 3

What will be the result of this query?

UPDATE products SET price = price + 2 WHERE price < 10;

medium

A. All products will have their price increased by 2.

B. Only products with price less than 10 will have their price increased by 2.

C. No products will be updated because price is not changed.

D. Syntax error due to missing WHERE clause.

Solution

1. Step 1: Identify rows matching WHERE condition

   Prices less than 10 are 5 and 3 (Pencil and Eraser).

2. Step 2: Apply UPDATE only to matching rows

   Only Pencil and Eraser prices increase by 2, Pen remains 10.

3. Final Answer:

   Only products with price less than 10 will have their price increased by 2. -> Option B

4. Quick Check:

   WHERE filters rows updated [OK]

Hint: WHERE limits which rows get updated, others stay same [OK]

Common Mistakes:

• Assuming all rows update without WHERE
• Thinking price must be reset, not incremented
• Confusing syntax error with correct query

4.

Find the error in this query:

UPDATE employees SET salary = 6000 WHERE;

medium

A. Missing condition after WHERE clause.

B. Missing SET keyword.

C. Incorrect table name.

D. No error, query is correct.

Solution

1. Step 1: Analyze the WHERE clause

   The WHERE clause is incomplete; it must have a condition after it.

2. Step 2: Check other parts of query

   SET keyword and table name are correct; only WHERE is incomplete.

3. Final Answer:

   Missing condition after WHERE clause. -> Option A

4. Quick Check:

   WHERE needs a condition [OK]

Hint: WHERE must always have a condition after it [OK]

Common Mistakes:

• Leaving WHERE empty
• Confusing missing SET with WHERE error
• Assuming query runs without WHERE condition

5.

You have a table students with columns id, name, and grade. You want to increase the grade by 5 for all students who scored less than 50, but not exceed 50 after update. Which query correctly does this?

hard

A. UPDATE students SET grade = CASE WHEN grade + 5 > 50 THEN 50 ELSE grade + 5 END WHERE grade < 50;

B. UPDATE students SET grade = grade + 5 WHERE grade < 50 AND grade + 5 <= 50;

C. UPDATE students SET grade = grade + 5 WHERE grade < 50;

D. UPDATE students SET grade = 50 WHERE grade < 50;

Solution

1. Step 1: Understand the requirement

   Increase grade by 5 only for grades less than 50, but cap max grade at 50.

2. Step 2: Analyze each option

   UPDATE students SET grade = 50 WHERE grade < 50; sets all below 50 to 50 directly, no increase by 5. UPDATE students SET grade = grade + 5 WHERE grade < 50 AND grade + 5 <= 50; increases by 5 only if result ≤ 50, skipping some rows. UPDATE students SET grade = grade + 5 WHERE grade < 50; increases by 5 without capping at 50. UPDATE students SET grade = CASE WHEN grade + 5 > 50 THEN 50 ELSE grade + 5 END WHERE grade < 50; uses CASE to increase by 5 but caps at 50 correctly.

3. Final Answer:

   UPDATE students SET grade = CASE WHEN grade + 5 > 50 THEN 50 ELSE grade + 5 END WHERE grade < 50; -> Option A

4. Quick Check:

   Use CASE to cap values in UPDATE [OK]

Hint: Use CASE in UPDATE to handle conditional value changes [OK]

Common Mistakes:

• Not capping grade at 50
• Updating all rows without WHERE
• Skipping rows that would exceed 50