Fichas
Databases
Fichas del conjunto (8)
- 1—KEYS
Primary Key - uniquely identifies each record in the table
Secondary Key - an entity that could have been a primary key but isn't
Surrogate Key - a unique primary key that is not derived from any data in the database and whose only significance is to act as the primary key
Compound Key - consists of more than on attribute to uniquely identify an entity occurrence. - 2NORMALISATION1NF
- no columns with repeated or similar data
- each data item cannont be broken
-each row is unique
- each field has a unique name - 3...NORMALISATOIN2NF
-in first normal form
- non-key attributes must depend on every part of the primary key - 4...NORMALISATION3NF
-in second normal form
- no non-key attribute that depend on another non-key attribute
- link attirubutes together to obtain the information without making it redundant with, with new tables and secondary keys - 5STRUCTURED QUERY LANGUAGESQL is an example of a declarative language. Statements in SQL describe what we want but leave the software to deal with the rest of the process.
- 6DDL - Data Definition LanguageA command language that helps you to create, delete and alter the database.
E.g CREATE - 7DML - Data Manipulation LanguageA language that supports the manipulation and processing of the data, this includes insering, deleting, updating and processing data.
E.g. SELECT ... FROM ... WHERE - 8Data DictionaryDescribes the structure and attributes of data 'items' to be used within a software application.
Includes the name, data type, field length and other other things such as validation of fields in a table.
Información
- Descripción
- Fichas sobre Databases, creado por katie.ricketts el 25/09/2013.
- Creado por
- katie.ricketts
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