La mayor parte de este libro trata sobre cómo leer datos de una base de datos con consultas SQL. La lectura es una de las cuatro operaciones básicas de las bases de datos, además de crear, leer, actualizar y eliminar (CRUD).
Una base de datos es un lugar donde almacenar datos de forma organizada.
Dentro de una base de datos, puedes crear objetos de base de datos, que son cosas que almacenan o hacen referencia a datos. Los objetos de base de datos más comunes son las tablas, las restricciones, los índices y las vistas.
Un modelo de datos o un esquema describe cómo se organizan los objetos de una base de datos.
La Figura 5-1 muestra una base de datos que contiene muchas tablas. Los detalles sobre cómo se definen las tablas (por ejemplo, la tabla Sales contiene cinco columnas) y cómo se conectan entre sí (por ejemplo, la columna customer_id de la tabla Sales coincide con la columna customer_id de la tabla Customer ) forman parte del esquema de la base de datos.
Figura 5-1. Una base de datos con un esquema en ...
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