Designing Data-Intensive Applications – Data Models: Query Languages

We dive into declarative vs imperative query languages as we continue to dive into Designing Data-Intensive Applications while Allen is gallivanting around London, Michael had a bullish opinion, and Joe might not know about The Witcher.

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Query Languages

Declarative vs Imperative

• The relational model introduced a declarative query language: SQL.
• Prior models used imperative code.
• An imperative language performs certain operations in a certain order, i.e. do this, then do that.
• With a declarative query language, you specify the pattern of data you want, the conditions that must be met, any sorting, grouping, etc.
  • Note that you don't specify how to retrieve the data. That is left to the optimizer to figure out.
• Declarative languages are attractive because they are shorter and easier to work with.
  • Consider UI frameworks where you declaratively describe the UI without needing to write code that actually draws a button of a specific size in a specific place with a specific label, etc.
• Additionally,