JSONB containment (@>) operator in PostgreSQL

Introduction

The JSONB containment operator @> helps you check if one JSONB data contains another. It is like asking, "Does this box have everything that this smaller box has inside?"

You want to find all records where a JSONB column includes a specific key-value pair.

You need to filter data that contains certain nested JSON objects.

You want to quickly check if a JSONB document has a particular structure or data inside.

You are searching for users who have specific preferences stored in a JSONB column.

You want to match JSONB data that contains a subset of keys and values.

Syntax

PostgreSQL

jsonb_column @> jsonb_value

The left side must be a JSONB column or expression.

The right side is the JSONB value you want to check if it is contained inside the left side.

Examples

Checks if the JSONB column data contains the key name with value Alice.

PostgreSQL

data @> '{"name": "Alice"}'::jsonb

Finds rows where the JSONB column data has an age key with value 30.

PostgreSQL

data @> '{"age": 30}'::jsonb

Checks if data contains an address object with a city key equal to Paris.

PostgreSQL

data @> '{"address": {"city": "Paris"}}'::jsonb

Sample Program

This example creates a table with a JSONB column and inserts three people with different info. Then it selects those whose age is 30 using the @> operator.

PostgreSQL

CREATE TABLE people (id SERIAL PRIMARY KEY, info JSONB);

INSERT INTO people (info) VALUES
  ('{"name": "Alice", "age": 30, "city": "Paris"}'::jsonb),
  ('{"name": "Bob", "age": 25, "city": "London"}'::jsonb),
  ('{"name": "Carol", "age": 30, "city": "Paris", "hobby": "reading"}'::jsonb);

SELECT id, info FROM people WHERE info @> '{"age": 30}'::jsonb;

Important Notes

The @> operator works only with JSONB data type, not plain JSON.

It checks if the right JSONB is contained anywhere inside the left JSONB, including nested objects.

Use ::jsonb to cast text to JSONB when writing queries.

Summary

The @> operator checks if one JSONB contains another.

It is useful to filter rows based on JSONB content.

Remember to cast strings to JSONB using ::jsonb in queries.

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