JSON vs JSONB differences in PostgreSQL

Introduction

JSON and JSONB are two ways to store JSON data in PostgreSQL. Knowing their differences helps you choose the best one for your needs.

When you want to store JSON data as text and keep the original formatting.

When you want to store JSON data in a way that is faster to query and index.

When you need to update parts of JSON data efficiently.

When you want to save space by removing extra spaces and ordering keys.

When you want to perform complex searches inside JSON data quickly.

Syntax

PostgreSQL

CREATE TABLE example_json (
  data JSON
);

CREATE TABLE example_jsonb (
  data JSONB
);

JSON stores data as plain text, preserving formatting.

JSONB stores data in a binary format, optimized for searching and indexing.

Examples

Insert JSON data as text into a JSON column.

PostgreSQL

INSERT INTO example_json (data) VALUES ('{"name": "Alice", "age": 30}');

Insert JSON data into a JSONB column; PostgreSQL converts it to binary format.

PostgreSQL

INSERT INTO example_jsonb (data) VALUES ('{"name": "Alice", "age": 30}');

Query JSONB data to find rows where age is 30 and get the name.

PostgreSQL

SELECT data->>'name' FROM example_jsonb WHERE data @> '{"age": 30}';

Sample Program

This example shows creating tables with JSON and JSONB columns, inserting data, and querying each type. JSON query uses text matching, JSONB query uses JSON containment operator.

PostgreSQL

CREATE TABLE people_json (
  info JSON
);

CREATE TABLE people_jsonb (
  info JSONB
);

INSERT INTO people_json (info) VALUES
  ('{"name": "Bob", "city": "NY"}'),
  ('{"name": "Carol", "city": "LA"}');

INSERT INTO people_jsonb (info) VALUES
  ('{"name": "Bob", "city": "NY"}'),
  ('{"name": "Carol", "city": "LA"}');

-- Query JSON data (text search)
SELECT info->>'name' AS name FROM people_json WHERE info::text LIKE '%NY%';

-- Query JSONB data (index search)
SELECT info->>'name' AS name FROM people_jsonb WHERE info @> '{"city": "NY"}';

Important Notes

JSONB supports indexing, which makes queries faster.

JSON preserves the exact text, including spaces and order of keys.

JSONB removes duplicate keys and orders keys internally.

Summary

JSON stores data as plain text, keeping formatting.

JSONB stores data in binary, optimized for speed and indexing.

Use JSONB when you need fast queries and updates on JSON data.

Practice

1. Which of the following is a key difference between json and jsonb data types in PostgreSQL?

easy

A. json stores data as plain text, while jsonb stores data in a binary format.

B. jsonb preserves whitespace and formatting, json does not.

C. json supports indexing, jsonb does not.

D. jsonb cannot store nested objects, json can.

Solution

1. Step 1: Understand storage formats

   json stores JSON data as plain text, preserving the original formatting including whitespace.

2. Step 2: Understand jsonb storage

   jsonb stores JSON data in a binary format optimized for faster processing and indexing.

3. Final Answer:

   json stores data as plain text, while jsonb stores data in a binary format. -> Option A

4. Quick Check:

   Storage format difference = Option A [OK]

Hint: Remember: json = text, jsonb = binary for speed [OK]

Common Mistakes:

• Thinking jsonb preserves whitespace like json
• Assuming jsonb cannot index data
• Believing jsonb cannot store nested objects

2. Which of the following is the correct way to declare a column with jsonb type in PostgreSQL?

easy

A. CREATE TABLE data (info JSONB);

B. CREATE TABLE data (info JSONB[]);

C. CREATE TABLE data (info JSON);

D. CREATE TABLE data (info BINARYJSON);

Solution

1. Step 1: Review PostgreSQL syntax for JSONB

   The correct data type name is jsonb (case-insensitive), used directly as a column type.

2. Step 2: Check each option

   Option A uses JSONB correctly. Option A tries to declare an array of jsonb, which is valid but not the simplest declaration. Option A uses JSON type, not jsonb. Option A uses a non-existent type BINARYJSON.

3. Final Answer:

   CREATE TABLE data (info JSONB); -> Option A

4. Quick Check:

   Correct jsonb column syntax = Option A [OK]

Hint: Use JSONB directly as column type, no extra keywords [OK]

Common Mistakes:

• Confusing JSON and JSONB types
• Using invalid type names like BINARYJSON
• Adding unnecessary array brackets

3. Given the table items with a json column data storing '{"a":1, "b":2}', what will this query return?

SELECT data @> '{"a":1}'::jsonb FROM items;

medium

A. Error because data is json, but query uses jsonb operator

B. True for rows where data contains key "a" with value 1

C. False for all rows because data is json, not jsonb

D. Returns all rows regardless of content

Solution

1. Step 1: Understand operator compatibility

   The @> operator is defined for jsonb types, not for json. Using it on a json column causes an error.

2. Step 2: Analyze the query

   The query tries to use @> on data which is json, but the right side is cast to jsonb. This mismatch causes a type error.

3. Final Answer:

   Error because data is json, but query uses jsonb operator -> Option A

4. Quick Check:

   jsonb operator on json column = Error [OK]

Hint: jsonb operators need jsonb columns, not json [OK]

Common Mistakes:

• Assuming json and jsonb are interchangeable
• Ignoring type casting errors
• Expecting operator to work on json type

4. You have a table with a jsonb column but your query is slow when filtering by keys. What is the most likely cause?

medium

A. No GIN or BTREE index on the jsonb column

B. Using json type instead of jsonb

C. The JSON data is stored as plain text

D. The query uses LIKE operator on the jsonb column

Solution

1. Step 1: Understand indexing for jsonb

   jsonb supports GIN or BTREE indexes to speed up key/value lookups.

2. Step 2: Identify cause of slow queries

   If no index exists on the jsonb column, queries filtering by keys must scan all rows, causing slowness.

3. Final Answer:

   No GIN or BTREE index on the jsonb column -> Option A

4. Quick Check:

   Missing index on jsonb = slow queries [OK]

Hint: Add GIN index on jsonb for fast key lookups [OK]

Common Mistakes:

• Confusing json and jsonb types
• Using LIKE on jsonb instead of jsonb operators
• Ignoring indexing for jsonb columns

5. You want to store JSON data and frequently query nested keys with fast performance. Which approach is best?

hard

A. Store data as json and create expression indexes on keys

B. Store data as jsonb and create a GIN index on the column

C. Store data as text and parse JSON in application code

D. Store data as jsonb but avoid indexes for faster inserts

Solution

1. Step 1: Choose data type for fast queries

   jsonb is optimized for querying and indexing nested JSON data.

2. Step 2: Use appropriate indexing

   Creating a GIN index on the jsonb column enables fast key and path lookups.

3. Final Answer:

   Store data as jsonb and create a GIN index on the column -> Option B

4. Quick Check:

   jsonb + GIN index = best for fast nested queries [OK]

Hint: Use jsonb with GIN index for fast nested JSON queries [OK]

Common Mistakes:

• Using json type which is slower for queries
• Avoiding indexes to speed inserts but hurting queries
• Parsing JSON outside database causing overhead