JSONB modification functions in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a new key-value pair to a JSONB column.

PostgreSQL

UPDATE users SET data = data || '{"[1]": "active"}' WHERE id = 1;

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

Aemail

Bstatus

Cname

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Using a key that does not exist or is unrelated.

Forgetting to use double quotes around the key.

The || operator merges JSONB objects. Adding "status": "active" updates the JSONB column with a new key-value pair.

2fill in blank

medium

Complete the code to remove the key 'age' from the JSONB column.

PostgreSQL

UPDATE users SET data = data - '[1]' WHERE id = 2;

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

Aage

Bstatus

Cemail

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Removing the wrong key.

Using quotes incorrectly around the key.

The - operator removes a key from a JSONB object. Here, it removes the key "age".

3fill in blank

hard

Fix the error in the code to update the 'email' key inside the JSONB column.

PostgreSQL

UPDATE users SET data = jsonb_set(data, '{"[1]"}', '"[e-mail]"') WHERE id = 3;

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

Aemail

Bstatus

Cage

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using a plain string instead of an array for the path.

Forgetting to quote the key inside the path.

The jsonb_set function updates a value at a specified path. The path must be an array of keys, so {"email"} is correct.

4fill in blank

hard

Fill both blanks to update the nested key 'city' inside the 'address' object in JSONB.

PostgreSQL

UPDATE users SET data = jsonb_set(data, '[1]', '"New York"') WHERE id = 4 AND data->'[2]' IS NOT NULL;

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

A{ "address", "city" }

Baddress

Ccity

D{ "city" }

Attempts:

3 left

💡 Hint

Common Mistakes

Using a single key instead of an array for the path.

Checking the wrong key in the WHERE clause.

The path to update a nested key must be an array of keys: {"address", "city"}. The condition checks if the 'address' key exists.

5fill in blank

hard

Fill all three blanks to insert a new key 'phone' with value '123-456' into the JSONB column only if it does not exist.

PostgreSQL

UPDATE users SET data = CASE WHEN NOT data ? '[1]' THEN jsonb_set(data, '[2]', '"[3]"') ELSE data END WHERE id = 5;

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

Aphone

B{ "phone" }

C123-456

Demail

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong key in the existence check.

Incorrect path format for jsonb_set.

Forgetting to quote the value as a JSON string.

The ? operator checks if a key exists. If 'phone' does not exist, jsonb_set adds it at path {"phone"} with value "123-456".

Practice

1. What does the PostgreSQL function jsonb_set do when used on a JSONB column?

easy

A. It creates a new JSONB column in the table.

B. It deletes the entire JSONB column from the table.

C. It converts JSONB data into plain text format.

D. It updates or adds a value at a specified path inside the JSONB data.

Solution

1. Step 1: Understand the purpose of jsonb_set

   The function jsonb_set is designed to update or add a value at a specific location inside JSONB data using a path.

2. Step 2: Compare with other options

   The other options describe actions unrelated to jsonb_set's purpose, such as creating or deleting columns or converting data types.

3. Final Answer:

   It updates or adds a value at a specified path inside the JSONB data. -> Option D

4. Quick Check:

   jsonb_set updates JSONB data [OK]

Hint: jsonb_set changes or adds JSONB values at paths [OK]

Common Mistakes:

• Thinking jsonb_set deletes data
• Confusing jsonb_set with data type conversion
• Assuming jsonb_set creates new columns

2. Which of the following is the correct syntax to remove a key named "age" from a JSONB column data in PostgreSQL?

easy

A. UPDATE table SET data = data - 'age';

B. UPDATE table SET data = jsonb_set(data, '{age}', NULL);

C. UPDATE table SET data = data + 'age';

D. UPDATE table SET data = jsonb_remove(data, 'age');

Solution

1. Step 1: Identify the correct operator for key removal

   In PostgreSQL, the minus operator (-) removes a key from JSONB data, so data - 'age' removes the key "age".

2. Step 2: Check other options for correctness

   UPDATE table SET data = jsonb_set(data, '{age}', NULL); tries to set the key to NULL but does not remove it. UPDATE table SET data = data + 'age'; adds a key, which is incorrect. UPDATE table SET data = jsonb_remove(data, 'age'); uses a non-existent function jsonb_remove.

3. Final Answer:

   UPDATE table SET data = data - 'age'; -> Option A

4. Quick Check:

   Minus operator removes JSONB key [OK]

Hint: Use minus (-) operator to remove JSONB keys [OK]

Common Mistakes:

• Using jsonb_set with NULL to remove keys
• Trying to add keys to remove them
• Using non-existent functions like jsonb_remove

3. Given the JSONB column data with value '{"name": "Alice", "details": {"age": 30}}', what will be the result of this query?

SELECT jsonb_set(data, '{details,age}', '31', false) FROM table;

medium

A. {"name": "Alice", "details": {"age": 31}}

B. {"name": "Alice", "details": {"age": "31"}}

C. {"name": "Alice", "details": {"age": 30}}

D. {"name": "Alice", "details": {"age": null}}

Solution

1. Step 1: Understand jsonb_set parameters

   The function jsonb_set updates the value at path '{details,age}' to '31' (a JSON string) because the new value is given as text, not as a number.

2. Step 2: Check the effect of the 'create_missing' flag

   The last parameter is false, so it updates existing key without creating new ones. The age key is updated to the string '31', not the number 31.

3. Final Answer:

   {"name": "Alice", "details": {"age": "31"}} -> Option B

4. Quick Check:

   jsonb_set updates value as text unless cast [OK]

Hint: jsonb_set inserts text values unless cast to JSONB [OK]

Common Mistakes:

• Assuming '31' is numeric without casting
• Expecting no change when create_missing is false
• Confusing JSON string and number types

4. You want to update a nested key in a JSONB column but your query

UPDATE table SET data = jsonb_set(data, '{info,score}', 100);

throws an error. What is the likely cause?

medium

A. The new value 100 is not cast to JSONB, causing a type error.

B. The path '{info,score}' is invalid syntax and must be a string.

C. jsonb_set cannot update nested keys, only top-level keys.

D. The data column is not JSONB type.

Solution

1. Step 1: Check the new value type in jsonb_set

   The third argument must be JSONB type. Passing 100 as an integer without casting causes a type error.

2. Step 2: Verify other options

   The path '{info,score}' is invalid syntax and must be a string. is incorrect because the path syntax is valid. jsonb_set cannot update nested keys, only top-level keys. is false; jsonb_set supports nested keys. The data column is not JSONB type. might cause error but question implies the error is from the query syntax.

3. Final Answer:

   The new value 100 is not cast to JSONB, causing a type error. -> Option A

4. Quick Check:

   jsonb_set value must be JSONB type [OK]

Hint: Cast new value to JSONB to avoid type errors [OK]

Common Mistakes:

• Passing plain integers without casting
• Misunderstanding path syntax
• Assuming jsonb_set can't update nested keys

5. You have a JSONB column data storing user info. You want to increment the "visits" count inside "stats" by 1, but visits might be missing. Which query correctly updates data to add or increment visits?

hard

A. UPDATE table SET data = data || '{"stats":{"visits":1}}';

B. UPDATE table SET data = jsonb_set(data, '{stats,visits}', '1');

C. UPDATE table SET data = jsonb_set(data, '{stats,visits}', to_jsonb((COALESCE((data->'stats'->>'visits')::int, 0) + 1)));

D. UPDATE table SET data = jsonb_set(data, '{visits}', to_jsonb(1));

Solution

1. Step 1: Understand the need to increment or add visits

   The query must get the current visits count, convert it to integer, handle missing key with COALESCE to 0, add 1, then convert back to JSONB.

2. Step 2: Analyze each option

   UPDATE table SET data = jsonb_set(data, '{stats,visits}', to_jsonb((COALESCE((data->'stats'->>'visits')::int, 0) + 1))); correctly uses COALESCE and to_jsonb to update visits inside stats. UPDATE table SET data = jsonb_set(data, '{stats,visits}', '1'); sets visits to string '1' always. UPDATE table SET data = data || '{"stats":{"visits":1}}'; overwrites stats with visits=1, losing other keys. UPDATE table SET data = jsonb_set(data, '{visits}', to_jsonb(1)); updates visits at top level, not inside stats.

3. Final Answer:

   UPDATE table SET data = jsonb_set(data, '{stats,visits}', to_jsonb((COALESCE((data->'stats'->>'visits')::int, 0) + 1))); -> Option C

4. Quick Check:

   Use COALESCE and to_jsonb for safe increment [OK]

Hint: Use COALESCE and cast to increment JSONB numbers safely [OK]

Common Mistakes:

• Overwriting nested objects accidentally
• Not casting string to int before increment
• Updating wrong JSONB path