GraphQL

• Query language and runtime for web APIs. 
• Developed by FB.
• While typical REST APIs require loading from multiple URLs, GraphQL APIs get all the data your app needs in a single request. Apps using GraphQL can be quick even on slow mobile network connections.
• A GraphQL server can process a client query using data from separate sources and present the results in a unified graph.
• GraphQL is a data query and manipulation language that allows specifying what data is to be retrieved ("declarative data fetching") or modified. 
• https://graphql.org/
• Graphql is a middleware as it can hide heterogeneous data sources like using RDB, Nosql, S3 together from frontend. This is also called database-diagnostic.
• Why People Use GraphQL for Relational Data Relational databases are built on relationships (Foreign Keys), and GraphQL is built on graphs.
• In a REST API, getting a user, their posts, and the comments on those posts might require three different API calls. In GraphQL, you write one query, and the backend handles the relational complexity in one go.

• When you use it with a relational database, the process typically looks like this:  

  1. The Schema: You define a GraphQL schema that mirrors your database tables (e.g., User, Post, Comment).

  2. The Resolvers: You write "resolver" functions. When a user asks for a User, the resolver runs a SQL query like SELECT * FROM users WHERE id = 1.  

  3. The Mapping: If a user asks for a User and their Posts, the resolver handles the "Join" logic, fetching the related data from the posts table.