Egor Urvanov

SQL

Specs and architecture

A declarative language for querying relational databases. A query says which data is needed, “room 5 bookings for tomorrow”, and the database itself decides how to fetch it, by index or by scanning. CHECK, UNIQUE and EXCLUDE constraints set rules the database enforces on every write, so they can be checked from the schema text.

what: the queryroom 5 bookings for tomorrowhow: the database decidesby index or by scanningresult rowsCHECK, UNIQUE, EXCLUDE: rules the database enforces on every write● model, people, systems, data  ● agent and harnessThe query says which data is needed, and the database picks how to fetch it

Source: Wikipedia: SQL

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