Transcript of Copy of Unit 18 P1.

Added on - 16 Sep 2019

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Transcript of Copy of Unit 18 P1Entities can be related to each other through the Primary Key and Foreign Keybecause, instead of typing the entities all over again you can use a key on anotherpart of a database and link the entities through it.What are Relationships?What do they do?What is a Primary Key?What advantages are there with using a database1. Databases save time. Retrieving a single record, which may take several minutesof digging in a paper-based filing system, can be done with just a few clicks in acomputerized database. Merging database records with documents makesproducing paper reports almost instantaneous2. Databases give you lots of different ways to look at your data. A request for aspecific answer or list from your database called a "query" can take just a minute ortwo to write, as opposed to hand-collating data records or sorting and resorting aspreadsheetUnit 18 P14. Well organized system which enable you to search for a particular name in themost quickest wayA primary key is a unique identifier for a database record. For example, When atable is created one of the fields is assigned as the primary key. While the primarykey is often a number, it may also be a text field or other data type.What is a Foreign Key?A Foreign Key is a key that is a column of groups or a group of columns in arelational database table that provides a link between data in two table. For exampleyou may link a ID (Primary Key of a section) to another part of a database and then itwill make a copy of an id and will then be transferred as a Foreign key.A one-to-many relationship occurs when a parent record in one table can potentiallyreference several child records in another table. In a one-to-many relationship, theparent is not required to have child records; therefore, the one-to-many relationshipallows zero child records, a single child record or multiple child records. Theimportant thing is that the child cannot have more than one parent record.
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