JSONB containment (@>) operator in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select rows where the JSONB column 'data' contains the key 'name'.

PostgreSQL

SELECT * FROM users WHERE data [1] '{"name": "John"}';

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

A@>

B->>

C->

D<@

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<@' which checks the opposite containment direction.

Using '->' or '->>' which extract JSON fields but do not check containment.

The @> operator checks if the left JSONB contains the right JSONB. Here, it finds rows where 'data' contains the key 'name' with value 'John'.

2fill in blank

medium

Complete the code to find rows where the JSONB column 'info' contains the key-value pair 'age': 30.

PostgreSQL

SELECT * FROM profiles WHERE info [1] '{"age": 30}';

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

A@>

B<@

C->

D->>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '->' which extracts a field but does not check containment.

Using '<@' which checks if right contains left, the opposite direction.

The @> operator checks if 'info' contains the key 'age' with value 30.

3fill in blank

hard

Fix the error in the query to correctly check if 'attributes' JSONB contains the key 'color' with value 'red'.

PostgreSQL

SELECT * FROM items WHERE attributes [1] '{"color": "red"}';

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

A<@

B@>

C->

D->>

Attempts:

3 left

💡 Hint

Common Mistakes

Using single quotes inside JSON keys instead of double quotes.

Using '<@' which checks containment in the wrong direction.

The operator @> is correct for containment. Also, the JSON must be valid with double quotes around keys and strings.

4fill in blank

hard

Fill both blanks to select rows where 'profile' JSONB contains the key 'status' with value 'active' and the key 'score' with value greater than 50.

PostgreSQL

SELECT * FROM users WHERE profile [1] '{"status": "active"}' AND (profile->>'score')::int [2] 50;

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

A@>

B>

C<

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' instead of '>' for numeric comparison.

Using '<@' instead of '@>' for containment.

The @> operator checks if 'profile' contains the key 'status' with value 'active'. The operator > compares the 'score' string value numerically (after casting) to 50.

5fill in blank

hard

Fill all three blanks to create a query that selects rows where 'details' JSONB contains 'type' equal to 'premium', 'active' equal to true, and 'visits' greater than 100.

PostgreSQL

SELECT * FROM accounts WHERE details [1] '{"type": "premium", "active": true}' AND (details->>[2])::int [3] 100;

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

A@>

B"visits"

C>

D"score"

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong key name like 'score' instead of 'visits'.

Not casting the extracted text to integer before comparison.

The @> operator checks if 'details' contains the keys 'type' and 'active' with specified values. The key 'visits' is extracted as text, cast to integer, and compared with '>' to 100.

Practice

1.

What does the PostgreSQL @> operator do when used with JSONB data?

easy

A. Checks if the right JSONB contains the left JSONB

B. Deletes the right JSONB from the left JSONB

C. Merges two JSONB objects into one

D. Checks if the left JSONB contains the right JSONB

Solution

1. Step 1: Understand the operator's purpose

   The @> operator in PostgreSQL is used to check containment between JSONB values.

2. Step 2: Identify the direction of containment

   It checks if the JSONB on the left side contains the JSONB on the right side.

3. Final Answer:

   Checks if the left JSONB contains the right JSONB -> Option D

4. Quick Check:

   JSONB containment = left contains right [OK]

Hint: Remember: left @> right means left contains right [OK]

Common Mistakes:

• Confusing which side contains which
• Thinking it merges JSONB objects
• Assuming it deletes data

2.

Which of the following is the correct syntax to check if a JSONB column data contains the JSON {"key": "value"}?

SELECT * FROM table WHERE data ___ '{"key": "value"}'::jsonb;

easy

A. @>

B. <@

C. ->

D. ->>

Solution

1. Step 1: Identify the containment operator

   The @> operator checks if the left JSONB contains the right JSONB.

2. Step 2: Apply correct syntax

   To check if data contains the JSON, use data @> '{"key": "value"}'::jsonb.

3. Final Answer:

   @> -> Option A

4. Quick Check:

   Containment operator = @> [OK]

Hint: Use @> with right side cast to jsonb [OK]

Common Mistakes:

• Using <@ which reverses containment
• Using -> or ->> which access keys, not contain
• Forgetting to cast string to jsonb

3.

Given the table items with a JSONB column attributes, what will this query return?

SELECT id FROM items WHERE attributes @> '{"color": "red"}'::jsonb;

Assuming items contains:

id | attributes
---+-------------------------
1  | {"color": "red", "size": "M"}
2  | {"color": "blue", "size": "L"}
3  | {"color": "red"}
4  | {"size": "S"}

medium

A. [4]

B. [2, 4]

C. [1, 3]

D. [1, 2, 3]

Solution

1. Step 1: Understand the query condition

   The query selects rows where attributes contain the JSON {"color": "red"}.

2. Step 2: Check each row's attributes

   Rows 1 and 3 have "color": "red"; rows 2 and 4 do not.

3. Final Answer:

   [1, 3] -> Option C

4. Quick Check:

   Only rows with color red = [1, 3] [OK]

Hint: Look for rows where JSON contains the key-value pair exactly [OK]

Common Mistakes:

• Including rows without the key-value pair
• Confusing @> with key existence operator
• Ignoring the JSONB cast requirement

4.

Identify the error in this query that tries to find rows where info JSONB column contains {"active": true}:

SELECT * FROM users WHERE info @> '{active: true}';

medium

A. Wrong operator used, should be <@

B. JSON keys must be in double quotes

C. Missing cast to jsonb for the right side

D. Boolean true must be in quotes

Solution

1. Step 1: Check JSON syntax correctness

   JSON keys must be enclosed in double quotes, so active should be "active".

2. Step 2: Verify casting and operator

   The query is missing ::jsonb cast, but the main syntax error is the missing quotes around the key.

3. Final Answer:

   JSON keys must be in double quotes -> Option B

4. Quick Check:

   JSON keys need double quotes [OK]

Hint: Always quote JSON keys and cast string to jsonb [OK]

Common Mistakes:

• Forgetting double quotes around keys
• Not casting string to jsonb
• Using wrong containment operator

5.

You want to find all rows in products where the details JSONB column contains {"features": {"waterproof": true}} and also the price is less than 100. Which query is correct?

hard

A. SELECT * FROM products WHERE details @> '{"features": {"waterproof": true}}'::jsonb AND price < 100;

B. SELECT * FROM products WHERE details <@ '{"features": {"waterproof": true}}'::jsonb AND price < 100;

C. SELECT * FROM products WHERE details @> '{features: {waterproof: true}}' AND price < 100;

D. SELECT * FROM products WHERE details -> 'features' @> '{"waterproof": true}' AND price < 100;

Solution

1. Step 1: Use correct containment operator and JSON syntax

   The @> operator checks if details contains the given JSON. The JSON must have keys in double quotes and be cast to jsonb.

2. Step 2: Combine with price condition

   Use AND price < 100 to filter by price.

3. Final Answer:

   SELECT * FROM products WHERE details @> '{"features": {"waterproof": true}}'::jsonb AND price < 100; -> Option A

4. Quick Check:

   Correct operator, JSON syntax, and price filter [OK]

Hint: Use @> with correct JSON and add AND for price filter [OK]

Common Mistakes:

• Using <@ instead of @>
• Missing quotes in JSON keys
• Incorrect JSONB casting
• Trying to use -> operator for containment