1720798
Descripción
Fichas por dominicbroadbent, actualizado hace más de 1 año
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Creado por dominicbroadbent
hace casi 10 años
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| Pregunta | Respuesta |
| Data Storage - Database Structure | A database is a system for managing a collection of data. Data is held in a table or grid. Every row of this table holds information on 1 particular thing e.g. a person (age,name etc) Every column of the table gives a single piece of info such as age or name. These properties are called fields. |
| Data Storage - Data Types | Text - A sequence of letters, numbers and other symbols. Multi-line text fields are often called memo fields. Numbers - Something that represents a numerical value, if it was typed using letters the prgram couldn't add it. e.g. stock numbers Data/Time - A combination of dates and times. Logical - Soemthing has to be true or false. For example, are you happy to recieve emails from us? Yes or No. |
| Data Storage - Database Relationships | All tables have a primary key on which they are organised. Every heading in a table will have a unique identifier e.g. amount of stock could be 300. The tables may also hold the primary keys of other tables(foreign keys) which can let you access a lot of information through one query. For example in our product table we could have a record of our stock and in our suplier table a record of their stock, when you enter the query "stock" you can access both sources of information at the same time. This link using a foreign key (stock) creates a relation between databases. You can have unlimited numbers of relationships. |
| Data Storage - Online Databases | Online databses are databases that can only be accessed over a network, these could be being updated by millions of users at a time. This data is accessed by a web server. There are sodtware which let you make these databses and some will incur a charge e.g. Office 365. The data is usually held by a hosting service. |
| Data Storage - Database Management Systems | Database Managment Systems are the programs that allow you to create and use databases. DBMS allows you to create, maintain, search and store data. It also allows multiple users to access the database at the same time and can provide different levels of access. SQL or Structured Query Language is the language useed to undertake the management activity. |
| Data Storage - DDL & DML | SQL is split into two parts; DDL and DML. Data Definition Language defines the structure of the database while Data Manipulation Language allows use to change, add, delete and query data. SQL generates the code that is used by the DBMS. |
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