Kleppmann, Martin

Query Languages for Data If you have a list of animal species and you want to return only the sharks in the list, a relational algebra expression would be \( \text{sharks} = \sigma_{\text{family = “Sharks”}}(\text{animals}) \). SQL queries follow the structure of relational algebra closely: SELECT * FROM animals WHERE family = 'Sharks'; … while an imperative query would be: function getSharks() { let sharks = []; for (let i = 0; i < animals....

Relational Model Versus Document Model; Thinking About Data Systems; Designing Data-Intensive Applications [Kleppmann, Martin]; Query Languages for Data; Reliability; Maintainability; Scalability;

A relational data model uses tables that consist of rows and columns. A row can be uniquely identified by a table + ID combination. A column entry can reference another row in another table through a shared key. One goal is to avoid duplicating data. However, to answer a real-world query, we end up paying th cost by joining results from multiple tables. That said, with proper indexing and prior research, combining results is pretty fast....