INSERT ON CONFLICT (upsert) in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to insert a new user with id 1 and name 'Alice'.

PostgreSQL

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

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

AWHERE id = 1

BON CONFLICT (id) DO UPDATE SET name = EXCLUDED.name

CON DUPLICATE KEY UPDATE name = 'Alice'

DON CONFLICT DO NOTHING

Attempts:

3 left

💡 Hint

Common Mistakes

Using MySQL syntax like ON DUPLICATE KEY UPDATE in PostgreSQL.

Forgetting the ON CONFLICT clause and causing errors on duplicates.

The ON CONFLICT DO NOTHING clause tells PostgreSQL to skip the insert if a conflict occurs on any unique constraint.

2fill in blank

medium

Complete the code to update the user's name to 'Bob' if the id conflicts.

PostgreSQL

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

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

ADO UPDATE SET name = EXCLUDED.name

BDO REPLACE

CDO NOTHING

DDO UPDATE SET name = 'Bob'

Attempts:

3 left

💡 Hint

Common Mistakes

Using DO NOTHING when an update is needed.

Trying to use DO REPLACE which is not valid in PostgreSQL.

The DO UPDATE SET name = EXCLUDED.name clause updates the existing row's name to the new value on conflict.

3fill in blank

hard

Fix the error in the code to update the user's email on conflict.

PostgreSQL

INSERT INTO users (id, email) VALUES (2, '[e-mail]') ON CONFLICT (id) DO UPDATE SET email = [1];

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

AEXCLUDED.email

Bemail

C'[e-mail]'

Dusers.email

Attempts:

3 left

💡 Hint

Common Mistakes

Using the column name without EXCLUDED, which refers to the old value.

Using a string literal instead of the new value.

Use EXCLUDED.email to refer to the new value being inserted during the conflict update.

4fill in blank

hard

Fill both blanks to insert or update the user's name and email on conflict.

PostgreSQL

INSERT INTO users (id, name, email) VALUES (3, 'Carol', '[e-mail]') ON CONFLICT (id) DO UPDATE SET name = [1], email = [2];

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

AEXCLUDED.name

B'Carol'

CEXCLUDED.email

Dusers.email

Attempts:

3 left

💡 Hint

Common Mistakes

Using string literals instead of EXCLUDED values.

Using table.column syntax which refers to old values.

Use EXCLUDED.name and EXCLUDED.email to update the existing row with the new values on conflict.

5fill in blank

hard

Fill all three blanks to insert or update the user's name, email, and age on conflict.

PostgreSQL

INSERT INTO users (id, name, email, age) VALUES (4, 'Dave', '[e-mail]', 30) ON CONFLICT (id) DO UPDATE SET name = [1], email = [2], age = [3];

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

AEXCLUDED.name

BEXCLUDED.email

CEXCLUDED.age

D'Dave'

Attempts:

3 left

💡 Hint

Common Mistakes

Using string literals instead of EXCLUDED values.

Forgetting to update all columns needed.

Use EXCLUDED.name, EXCLUDED.email, and EXCLUDED.age to update all columns with the new values on conflict.

Practice

1. What does the INSERT ON CONFLICT clause do in PostgreSQL?

easy

A. It inserts a new row or updates existing row if a conflict occurs.

B. It deletes rows that conflict with the new data.

C. It only inserts new rows and ignores conflicts without any update.

D. It creates a new table if a conflict is found.

Solution

1. Step 1: Understand the purpose and behavior of INSERT ON CONFLICT

   This clause helps handle duplicate key conflicts during insert operations by allowing an update instead of error. It either updates the existing row or ignores the insert, preventing errors.

2. Final Answer:

   It inserts a new row or updates existing row if a conflict occurs. -> Option A

3. Quick Check:

   INSERT ON CONFLICT = Insert or update [OK]

Hint: Think: insert new or update existing on conflict [OK]

Common Mistakes:

• Confusing ON CONFLICT with DELETE
• Assuming it only inserts without update
• Thinking it creates new tables

2. Which of the following is the correct syntax to update a column price on conflict for a table products with unique id?

easy

A. INSERT INTO products (id, price) VALUES (1, 100) ON CONFLICT DO NOTHING;

B. INSERT INTO products (id, price) VALUES (1, 100) ON DUPLICATE KEY UPDATE price = price + 1;

C. INSERT INTO products (id, price) VALUES (1, 100) ON CONFLICT (id) DO UPDATE SET price = EXCLUDED.price;

D. INSERT INTO products (id, price) VALUES (1, 100) ON CONFLICT (id) DO DELETE;

Solution

1. Step 1: Check PostgreSQL syntax for upsert and identify correct usage of EXCLUDED

   PostgreSQL uses ON CONFLICT (column) DO UPDATE SET with EXCLUDED to refer to new values. INSERT INTO products (id, price) VALUES (1, 100) ON CONFLICT (id) DO UPDATE SET price = EXCLUDED.price; correctly uses EXCLUDED.price to update the price on conflict of id.

2. Final Answer:

   INSERT INTO products (id, price) VALUES (1, 100) ON CONFLICT (id) DO UPDATE SET price = EXCLUDED.price; -> Option C

3. Quick Check:

   Correct syntax uses ON CONFLICT (id) DO UPDATE SET with EXCLUDED [OK]

Hint: Use EXCLUDED.column to update on conflict [OK]

Common Mistakes:

• Using MySQL syntax ON DUPLICATE KEY
• Forgetting EXCLUDED keyword
• Using DO DELETE which is invalid

3. Given the table users(id INT PRIMARY KEY, name TEXT, age INT) with data:
(1, 'Alice', 30)
What will be the result of this query?

INSERT INTO users (id, name, age) VALUES (1, 'Alice', 31) ON CONFLICT (id) DO UPDATE SET age = EXCLUDED.age RETURNING *;

medium

A. [] (empty result)

B. [{id:1, name:'Alice', age:31}]

C. Error: duplicate key value violates unique constraint

D. [{id:1, name:'Alice', age:30}]

Solution

1. Step 1: Understand the existing data/conflict and apply ON CONFLICT DO UPDATE

   Row with id=1 exists with age=30, new insert tries age=31 causing conflict on id. It updates age to EXCLUDED.age (31) and returns the updated row.

2. Final Answer:

   [{id:1, name:'Alice', age:31}] -> Option B

3. Quick Check:

   ON CONFLICT updates age to 31 and returns updated row [OK]

Hint: ON CONFLICT updates existing row and returns it [OK]

Common Mistakes:

• Expecting error on duplicate key
• Thinking old age remains unchanged
• Assuming empty result on update

4. Identify the error in this query:

INSERT INTO inventory (product_id, quantity) VALUES (10, 5) ON CONFLICT (product_id) DO UPDATE quantity = quantity + EXCLUDED.quantity;

medium

A. VALUES clause cannot be used with ON CONFLICT.

B. EXCLUDED keyword is not allowed in DO UPDATE.

C. ON CONFLICT must be followed by DO NOTHING, not DO UPDATE.

D. Missing SET keyword before update expressions.

Solution

1. Step 1: Review ON CONFLICT DO UPDATE syntax and identify missing SET keyword

   The DO UPDATE clause requires SET keyword before specifying column updates. The query misses SET before 'quantity = quantity + EXCLUDED.quantity', causing syntax error.

2. Final Answer:

   Missing SET keyword before update expressions. -> Option D

3. Quick Check:

   DO UPDATE requires SET before column assignments [OK]

Hint: Remember DO UPDATE SET column = value [OK]

Common Mistakes:

• Omitting SET keyword in DO UPDATE
• Misusing EXCLUDED keyword
• Confusing DO NOTHING and DO UPDATE

5. You want to insert a new user into users(id, name, score) but if the id exists, update the score only if the new score is higher. Which query correctly implements this?

hard

A. INSERT INTO users (id, name, score) VALUES (2, 'Bob', 50) ON CONFLICT (id) DO UPDATE SET score = EXCLUDED.score WHERE EXCLUDED.score > users.score;

B. INSERT INTO users (id, name, score) VALUES (2, 'Bob', 50) ON CONFLICT (id) DO UPDATE SET score = users.score WHERE EXCLUDED.score > users.score;

C. INSERT INTO users (id, name, score) VALUES (2, 'Bob', 50) ON CONFLICT (id) DO NOTHING WHERE EXCLUDED.score > users.score;

D. INSERT INTO users (id, name, score) VALUES (2, 'Bob', 50) ON CONFLICT (id) DO UPDATE SET score = EXCLUDED.score;

Solution

1. Step 1: Understand conditional update on conflict and use WHERE clause in DO UPDATE

   You want to update score only if new score is greater than existing score. INSERT INTO users (id, name, score) VALUES (2, 'Bob', 50) ON CONFLICT (id) DO UPDATE SET score = EXCLUDED.score WHERE EXCLUDED.score > users.score; uses WHERE EXCLUDED.score > users.score to conditionally update score correctly.

2. Final Answer:

   INSERT INTO users (id, name, score) VALUES (2, 'Bob', 50) ON CONFLICT (id) DO UPDATE SET score = EXCLUDED.score WHERE EXCLUDED.score > users.score; -> Option A

3. Quick Check:

   Conditional update uses WHERE clause in DO UPDATE [OK]

Hint: Use WHERE in DO UPDATE for conditional changes [OK]

Common Mistakes:

• Updating unconditionally without WHERE
• Using DO NOTHING with WHERE (invalid)
• Setting score to old value mistakenly