Inserting JSON data in PostgreSQL - Mini Project: Build & Apply

Inserting JSON Data into PostgreSQL

📖 Scenario: You are working on a small online bookstore database. You want to store book details in a table using JSON format to keep the data flexible and easy to update.

🎯 Goal: Create a table to store book information as JSON data, then insert a JSON record representing a book into the table.

📋 What You'll Learn

Create a table named books with a column info of type jsonb

Insert a JSON record into the books table with specific book details

Use exact JSON keys and values as specified

💡 Why This Matters

🌍 Real World

Storing flexible and complex data like book details in JSON format allows easy updates and schema changes without altering the database structure.

💼 Career

Many modern applications use JSON data types in databases like PostgreSQL to handle semi-structured data efficiently, a valuable skill for backend developers and database administrators.

1

Create the books table with a jsonb column

Write a SQL statement to create a table called books with one column named info of type jsonb.

PostgreSQL

-- Write the CREATE TABLE statement here
-- Your code here

Hint

Use CREATE TABLE books (info jsonb); to create the table.

2

Prepare the JSON data for insertion

Create a variable called book_json that holds the JSON data as a string with these exact key-value pairs: {"title": "The Great Gatsby", "author": "F. Scott Fitzgerald", "year": 1925}.

PostgreSQL

CREATE TABLE books (info jsonb);
-- Define the JSON string variable book_json here
-- Your code here

Hint

Use \set book_json '{"title": "The Great Gatsby", "author": "F. Scott Fitzgerald", "year": 1925}' to define the JSON string variable.

3

Insert the JSON data into the books table

Write an INSERT statement to add the JSON data stored in book_json into the info column of the books table. Use the ::jsonb cast to convert the string to JSONB.

PostgreSQL

CREATE TABLE books (info jsonb);
\set book_json '{"title": "The Great Gatsby", "author": "F. Scott Fitzgerald", "year": 1925}'
-- Insert the JSON data into books table here
-- Your code here

Hint

Use INSERT INTO books (info) VALUES (:book_json::jsonb); to insert the JSON data.

4

Verify the JSON data insertion

Write a SELECT statement to retrieve all rows from the books table to confirm the JSON data was inserted correctly.

PostgreSQL

CREATE TABLE books (info jsonb);
\set book_json '{"title": "The Great Gatsby", "author": "F. Scott Fitzgerald", "year": 1925}'
INSERT INTO books (info) VALUES (:book_json::jsonb);
-- Select all rows from books table here
-- Your code here

Hint

Use SELECT * FROM books; to see the inserted JSON data.

Practice

1. What is the correct way to insert JSON data into a PostgreSQL table with a json column named data?

easy

A. INSERT INTO table_name (data) VALUES (JSON('name: John, age: 30'));

B. INSERT INTO table_name (data) VALUES ({name: 'John', age: 30});

C. INSERT INTO table_name (data) VALUES ("{'name': 'John', 'age': 30}");

D. INSERT INTO table_name (data) VALUES ('{"name": "John", "age": 30}');

Solution

1. Step 1: Use single quotes for JSON string in SQL

   In PostgreSQL, JSON data must be enclosed in single quotes as a string literal.

2. Step 2: Use valid JSON format inside the string

   The JSON must have double quotes around keys and string values, like {"name": "John", "age": 30}.

3. Final Answer:

   INSERT INTO table_name (data) VALUES ('{"name": "John", "age": 30}'); -> Option D

4. Quick Check:

   JSON string with single quotes and double quotes inside = D [OK]

Hint: Always use single quotes around JSON string in SQL [OK]

Common Mistakes:

• Using double quotes for the whole JSON string
• Using unquoted keys or single quotes inside JSON
• Trying to insert JSON without quotes

2. Which of the following is the correct syntax to insert JSON data into a table named users with a jsonb column info?

easy

A. INSERT INTO users (info) VALUES (jsonb '{"city": "NY", "zip": 10001}');

B. INSERT INTO users (info) VALUES ('{city: "NY", zip: 10001}');

C. INSERT INTO users (info) VALUES ("{'city': 'NY', 'zip': 10001}");

D. INSERT INTO users (info) VALUES (jsonb '{city: NY, zip: 10001}');

Solution

1. Step 1: Use jsonb type cast for jsonb columns

   When inserting into a jsonb column, you can cast the string to jsonb using jsonb '...' .

2. Step 2: Use valid JSON string with double quotes inside single quotes

   The JSON must be valid with double quotes around keys and string values.

3. Final Answer:

   INSERT INTO users (info) VALUES (jsonb '{"city": "NY", "zip": 10001}'); -> Option A

4. Quick Check:

   jsonb cast with valid JSON string = C [OK]

Hint: Cast JSON string to jsonb with jsonb '...' for jsonb columns [OK]

Common Mistakes:

• Using double quotes for the whole JSON string
• Not casting to jsonb when required
• Using invalid JSON format without quotes

3. Given the table products with a json column details, what will be the result of this query?

INSERT INTO products (details) VALUES ('{"color": "red", "size": "M"}');
SELECT details->>'color' FROM products WHERE details->>'size' = 'M';

medium

A. ["M"]

B. [null]

C. ["red"]

D. Empty result

Solution

1. Step 1: Insert JSON with color and size keys

   The insert adds a row with details containing color: red and size: M.

2. Step 2: Select color where size equals 'M'

   The SELECT filters rows where details->>'size' = 'M' and returns details->>'color', which is 'red'.

3. Final Answer:

   ["red"] -> Option C

4. Quick Check:

   Filter by size 'M' returns color 'red' [OK]

Hint: Use ->> to get JSON text value for filtering and selecting [OK]

Common Mistakes:

• Using -> instead of ->> returns JSON, not text
• Expecting size value instead of color in output
• Not matching the filter condition correctly

4. You try to insert JSON data with this query:

INSERT INTO orders (info) VALUES ('{customer: "Alice", total: 50}');

But it fails. What is the error and how to fix it?

medium

A. Using double quotes inside JSON string; fix by using single quotes inside JSON.

B. Missing double quotes around JSON keys; fix by adding double quotes around keys.

C. JSON keys must be unquoted; fix by removing all quotes.

D. JSON must be cast to jsonb; fix by adding ::jsonb after string.

Solution

1. Step 1: Identify invalid JSON format

   JSON keys must be in double quotes, but here keys are unquoted (customer, total).

2. Step 2: Fix JSON by adding double quotes around keys

   Correct JSON is '{"customer": "Alice", "total": 50}'.

3. Final Answer:

   Missing double quotes around JSON keys; fix by adding double quotes around keys. -> Option B

4. Quick Check:

   JSON keys need double quotes = A [OK]

Hint: JSON keys must always be double-quoted strings [OK]

Common Mistakes:

• Using unquoted keys in JSON
• Mixing single and double quotes incorrectly
• Assuming casting fixes invalid JSON format

5. You want to insert multiple JSON objects into a table events with a jsonb column payload. Which query correctly inserts two JSON objects in one statement?

hard

A. INSERT INTO events (payload) VALUES (jsonb '{"type": "click", "x": 10}'), (jsonb '{"type": "scroll", "y": 20}');

B. INSERT INTO events (payload) VALUES '[{"type": "click", "x": 10}, {"type": "scroll", "y": 20}]';

C. INSERT INTO events (payload) VALUES (jsonb '[{"type": "click", "x": 10}, {"type": "scroll", "y": 20}]');

D. INSERT INTO events (payload) VALUES (jsonb '{type: click, x: 10}'), (jsonb '{type: scroll, y: 20}');

Solution

1. Step 1: Insert multiple rows with separate JSON objects

   Use multiple VALUES tuples, each with a valid JSON string cast to jsonb.

2. Step 2: Ensure JSON keys and strings are double-quoted

   Each JSON object must have keys and string values in double quotes inside single quotes.

3. Final Answer:

   INSERT INTO events (payload) VALUES (jsonb '{"type": "click", "x": 10}'), (jsonb '{"type": "scroll", "y": 20}'); -> Option A

4. Quick Check:

   Multiple rows with valid JSON objects = A [OK]

Hint: Use multiple VALUES tuples with jsonb cast for multiple JSON inserts [OK]

Common Mistakes:

• Trying to insert JSON array as one JSON object
• Using invalid JSON without quotes
• Not casting JSON string to jsonb when required