How to use SQLite's JSON extension?

SQLite's JSON extension provides the ability to process JSON data:

1. JSON Extension Overview

   • SQLite 3.38.0+ has built-in JSON1 extension
   • Provides a set of functions for creating, querying, and manipulating JSON data
   • JSON data is stored in the database as TEXT type

2. JSON Function Categories

   • Creation Functions: json_array(), json_object()
   • Extraction Functions: json_extract(), json_each()
   • Modification Functions: json_set(), json_remove()
   • Query Functions: json_array_length(), json_type()
   • Path Functions: json_patch(), json_tree()

3. Creating JSON Data

   sql
   -- Create JSON object
   SELECT json_object('name', 'Alice', 'age', 30);
   -- Output: {"name":"Alice","age":30}
   
   -- Create JSON array
   SELECT json_array(1, 2, 3, 'four');
   -- Output: [1,2,3,"four"]

4. Extracting JSON Data

   sql
   -- Extract JSON field
   SELECT json_extract('{"name":"Alice","age":30}', '$.name');
   -- Output: "Alice"
   
   -- Extract nested field
   SELECT json_extract('{"user":{"name":"Alice"}}', '$.user.name');
   -- Output: "Alice"

5. Modifying JSON Data

   sql
   -- Set or update JSON field
   SELECT json_set('{"name":"Alice"}', '$.age', 30);
   -- Output: {"name":"Alice","age":30}
   
   -- Remove JSON field
   SELECT json_remove('{"name":"Alice","age":30}', '$.age');
   -- Output: {"name":"Alice"}

6. Querying JSON Data

   sql
   -- Get JSON array length
   SELECT json_array_length('[1,2,3,4]');
   -- Output: 4
   
   -- Get JSON field type
   SELECT json_type('{"name":"Alice","age":30}', '$.age');
   -- Output: integer

7. Using JSON in Tables

   sql
   -- Create table with JSON field
   CREATE TABLE users (
       id INTEGER PRIMARY KEY,
       data TEXT
   );
   
   -- Insert JSON data
   INSERT INTO users (data) VALUES (json_object('name', 'Alice', 'tags', json_array('admin', 'user')));
   
   -- Query JSON data
   SELECT json_extract(data, '$.name') as name FROM users;
   
   -- Filter based on JSON field
   SELECT * FROM users WHERE json_extract(data, '$.name') = 'Alice';

8. JSON Path Expressions

   • $: Root object
   • .key: Object property
   • [index]: Array index
   • *: Wildcard
   • ..: Recursive descent

9. Performance Considerations

   • JSON queries are slower than direct column queries
   • Can use generated columns and indexes to optimize JSON queries

   sql
   CREATE TABLE users (
       id INTEGER PRIMARY KEY,
       data TEXT,
       name TEXT GENERATED ALWAYS AS (json_extract(data, '$.name')) STORED
   );
   CREATE INDEX idx_name ON users(name);

10. Use Cases

    • Store flexible data structures
    • Store configuration information
    • Store logs and metadata
    • Implement NoSQL-style data storage

JSON extension enables SQLite to handle semi-structured data, enhancing database flexibility.