August 2024
Intermediate to advanced
380 pages
10h 16m
Spanish
Content preview from Aprender SQL, 3ª Edición
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Capítulo 15. Metadatos Metadatos
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Además de almacenar todos los datos que los distintos usuarios introducen en una base de datos, un servidor de bases de datos también necesita almacenar información sobre todos los objetos de la base de datos (tablas, vistas, índices, etc.) que se crearon para almacenar estos datos. El servidor de bases de datos almacena esta información, como es lógico, en una base de datos. Este capítulo trata de cómo y dónde se almacena esta información, conocida como metadatos, cómo puedes acceder a ella y cómo puedes utilizarla para construir sistemas flexibles.
Datos sobre datos
Los metadatos son esencialmente datos sobre datos. Cada vez que creas un objeto de base de datos, el servidor de bases de datos necesita registrar diversos datos. Por ejemplo, si fueras a crear una tabla con varias columnas, una restricción de clave primaria, tres índices y una restricción de clave foránea, el servidor de la base de datos necesitaría almacenar toda la información siguiente:
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Nombre de la tabla
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Información de almacenamiento de la tabla (tablespace, tamaño inicial, etc.)
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Motor de almacenamiento
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Nombres de columna
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Tipos de datos de columna
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Valores de columna por defecto
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not nullrestricciones de columna -
Columnas de clave primaria
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Nombre de la clave primaria
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Nombre del índice de clave primaria
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Nombres índice
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Tipos de índice (árbol ...
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