ON DUPLICATE KEY UPDATE in MySQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to insert a new user or update the email if the user ID already exists.

MySQL

INSERT INTO users (id, name, email) VALUES (1, 'Alice', '[e-mail]') [1];

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

AWHERE id = 1

BSET email = '[e-mail]'

CON DUPLICATE KEY UPDATE email = '[e-mail]'

DUPDATE users SET email = '[e-mail]'

Attempts:

3 left

💡 Hint

Common Mistakes

Using WHERE clause after INSERT

Trying to use SET without ON DUPLICATE KEY UPDATE

Writing UPDATE statement instead of INSERT

The ON DUPLICATE KEY UPDATE clause allows updating the email if the user ID already exists.

2fill in blank

medium

Complete the code to update the user's name to 'Bob' if the ID already exists.

MySQL

INSERT INTO users (id, name) VALUES (2, 'Bob') [1];

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

AON DUPLICATE KEY UPDATE name = 'Bob'

BON DUPLICATE KEY UPDATE id = 2

CWHERE id = 2

DSET name = 'Bob'

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to update the ID column

Using WHERE clause incorrectly

Omitting the ON DUPLICATE KEY UPDATE clause

The ON DUPLICATE KEY UPDATE clause updates the name when the ID is a duplicate.

3fill in blank

hard

Fix the error in the code to update the email to '[e-mail]' on duplicate key.

MySQL

INSERT INTO users (id, email) VALUES (2, '[e-mail]') [1];

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

AON DUPLICATE UPDATE email = '[e-mail]'

BON DUPLICATE KEY UPDATE email = '[e-mail]'

CON DUPLICATE KEY SET email = '[e-mail]'

DON DUPLICATE KEY WHERE email = '[e-mail]'

Attempts:

3 left

💡 Hint

Common Mistakes

Using SET instead of UPDATE

Omitting KEY in the clause

Using WHERE clause incorrectly

The correct syntax is ON DUPLICATE KEY UPDATE followed by the column assignment.

4fill in blank

hard

Fill both blanks to insert a product or update its price and stock if the product ID exists.

MySQL

INSERT INTO products (id, price, stock) VALUES ([1], 100, 50) [2] price = 100, stock = 50;

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

A3

BON DUPLICATE KEY UPDATE

C5

DWHERE id = 3

Attempts:

3 left

💡 Hint

Common Mistakes

Using WHERE clause instead of ON DUPLICATE KEY UPDATE

Putting wrong ID value

Omitting the update clause

The product ID is 3, and the clause ON DUPLICATE KEY UPDATE updates price and stock if the ID exists.

5fill in blank

hard

Fill all three blanks to insert or update a user's name, email, and age on duplicate key.

MySQL

INSERT INTO users (id, name, email, age) VALUES ([1], [2], [3], 30) ON DUPLICATE KEY UPDATE name = [2], email = [3], age = 30;

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

A10

B'Charlie'

C'[e-mail]'

D'Charlie Brown'

Attempts:

3 left

💡 Hint

Common Mistakes

Using different values in insert and update parts

Omitting quotes around strings

Mixing up name and email positions

The user ID is 10, the name is 'Charlie', and the email is '[e-mail]'. The update clause uses the same values.

Practice

1. What does the ON DUPLICATE KEY UPDATE clause do in a MySQL INSERT statement?

easy

A. It deletes rows with duplicate keys before inserting new ones.

B. It updates existing rows if a duplicate key is found during insert.

C. It ignores the insert if a duplicate key exists.

D. It creates a new table when a duplicate key is found.

Solution

1. Step 1: Understand the purpose of ON DUPLICATE KEY UPDATE

   This clause allows an INSERT statement to update existing rows if a duplicate key (like a primary key) is found instead of causing an error.

2. Step 2: Compare options with this behavior

   Only It updates existing rows if a duplicate key is found during insert. correctly describes this behavior. The other options describe different actions that are not what this clause does.

3. Final Answer:

   It updates existing rows if a duplicate key is found during insert. -> Option B

4. Quick Check:

   ON DUPLICATE KEY UPDATE = update on duplicate [OK]

Hint: It updates rows when duplicate keys appear during insert [OK]

Common Mistakes:

• Thinking it deletes rows instead of updating
• Assuming it ignores duplicates silently
• Confusing it with creating new tables

2. Which of the following is the correct syntax to use ON DUPLICATE KEY UPDATE in MySQL?

easy

A. INSERT INTO table (id, val) VALUES (1, 'a') ON DUPLICATE KEY UPDATE val = 'b';

B. INSERT INTO table (id, val) VALUES (1, 'a') DUPLICATE KEY UPDATE val = 'b';

C. INSERT INTO table (id, val) VALUES (1, 'a') ON DUPLICATE UPDATE val = 'b';

D. INSERT INTO table (id, val) VALUES (1, 'a') ON DUPLICATE KEY SET val = 'b';

Solution

1. Step 1: Recall the correct syntax format

   The correct syntax is INSERT INTO ... VALUES (...) ON DUPLICATE KEY UPDATE column = value;

2. Step 2: Match options with correct syntax

   Only INSERT INTO table (id, val) VALUES (1, 'a') ON DUPLICATE KEY UPDATE val = 'b'; matches the exact syntax. The other options have incorrect keywords or missing parts.

3. Final Answer:

   INSERT INTO table (id, val) VALUES (1, 'a') ON DUPLICATE KEY UPDATE val = 'b'; -> Option A

4. Quick Check:

   Correct syntax includes 'ON DUPLICATE KEY UPDATE' [OK]

Hint: Remember full phrase: ON DUPLICATE KEY UPDATE [OK]

Common Mistakes:

• Omitting the word KEY
• Using UPDATE without ON DUPLICATE KEY
• Replacing UPDATE with SET

3. Given the table users(id INT PRIMARY KEY, name VARCHAR(20), points INT) with data:
(1, 'Alice', 10)
What will be the result after running?

INSERT INTO users (id, name, points) VALUES (1, 'Alice', 20) ON DUPLICATE KEY UPDATE points = points + 5;

medium

A. A new row with id=1 and points=20 is inserted.

B. The existing row with id=1 is updated to points=5.

C. The existing row with id=1 is updated to points=15.

D. The query causes a duplicate key error.

Solution

1. Step 1: Identify duplicate key and update action

   The id 1 already exists, so the ON DUPLICATE KEY UPDATE clause triggers. It updates points by adding 5 to the existing value.

2. Step 2: Calculate updated points value

   Existing points = 10, so new points = 10 + 5 = 15.

3. Final Answer:

   The existing row with id=1 is updated to points=15. -> Option C

4. Quick Check:

   points = 10 + 5 = 15 [OK]

Hint: Update adds to existing value on duplicate key [OK]

Common Mistakes:

• Thinking it inserts a new row instead of updating
• Assuming points become 20 instead of adding 5
• Expecting an error on duplicate key

4. What is wrong with this query?

INSERT INTO products (id, stock) VALUES (5, 10) ON DUPLICATE KEY UPDATE stock = stock + 1,;

medium

A. The VALUES keyword is not allowed with ON DUPLICATE KEY UPDATE.

B. The ON DUPLICATE KEY UPDATE clause is missing a column.

C. The stock column cannot be updated this way.

D. The comma before the semicolon causes a syntax error.

Solution

1. Step 1: Check syntax of ON DUPLICATE KEY UPDATE clause

   The clause ends with a comma before the semicolon, which is invalid syntax in SQL.

2. Step 2: Identify correct syntax rules

   There should be no trailing comma after the last update assignment.

3. Final Answer:

   The comma before the semicolon causes a syntax error. -> Option D

4. Quick Check:

   Trailing comma in UPDATE clause = syntax error [OK]

Hint: No trailing comma after last update assignment [OK]

Common Mistakes:

• Leaving a comma after last column update
• Confusing VALUES usage with ON DUPLICATE KEY UPDATE
• Thinking stock column can't be updated

5. You want to insert a new user or update their score only if the new score is higher than the existing one. Which query correctly uses ON DUPLICATE KEY UPDATE for this?

hard

A. INSERT INTO users (id, score) VALUES (2, 50) ON DUPLICATE KEY UPDATE score = IF(score < VALUES(score), VALUES(score), score);

B. INSERT INTO users (id, score) VALUES (2, 50) ON DUPLICATE KEY UPDATE score = VALUES(score);

C. INSERT INTO users (id, score) VALUES (2, 50) ON DUPLICATE KEY UPDATE score = score + VALUES(score);

D. INSERT INTO users (id, score) VALUES (2, 50) ON DUPLICATE KEY UPDATE score = score - VALUES(score);

Solution

1. Step 1: Understand the requirement

   We want to update the score only if the new score is greater than the existing score.

2. Step 2: Analyze each option's update logic

   INSERT INTO users (id, score) VALUES (2, 50) ON DUPLICATE KEY UPDATE score = VALUES(score); always replaces the score, ignoring if it's higher or not. INSERT INTO users (id, score) VALUES (2, 50) ON DUPLICATE KEY UPDATE score = IF(score < VALUES(score), VALUES(score), score); uses IF to update only if new score is higher. INSERT INTO users (id, score) VALUES (2, 50) ON DUPLICATE KEY UPDATE score = score + VALUES(score); adds scores, which is not the requirement. INSERT INTO users (id, score) VALUES (2, 50) ON DUPLICATE KEY UPDATE score = score - VALUES(score); subtracts scores, which is incorrect.

3. Final Answer:

   INSERT INTO users (id, score) VALUES (2, 50) ON DUPLICATE KEY UPDATE score = IF(score < VALUES(score), VALUES(score), score); -> Option A

4. Quick Check:

   Use IF to update only if new score is higher [OK]

Hint: Use IF(condition, new, old) to update conditionally [OK]

Common Mistakes:

• Always overwriting score without condition
• Adding scores instead of comparing
• Subtracting scores mistakenly