Koncepti relacionih baza podataka (The concepts of relational databases)

Koncepti relacionih baza podataka:

• tabele
• kolone
• redovi
• vrednosti
• kljucevi

Tabele - relacione baze podataka sastoje se od relacija (odnosa izmedju podataka). koje se zovu tabelama. Tabela je tabela podataka.

Kolone - tabela sadrzi kolone u koje su smestene odredjen vrste podataka. Kolone tabela se ponekad nazivaju polja ili atributi tabele. 

Redovi - svaki red u tabeli predstavlja po jednog kupca. Zbog tabelarnog formata svaki red ima iste atribute. Redovi tabela se zovu zapisi.

Vrednosti - svaki red se sastoji od skupa pojedinacnih vrednosti koje se nalaze u kolonama. Svaka vrednost mora imati tip podataka  odredjen kolonom u kojoj se nalazi.

Kljucevi - potrebno je da postoji nacin nedvosmislene identifikacije svakog kupca. Svakom kupcu dodelite jedinstven ID broj. ili sifru kupca. 

Identifikaciona kolona u tabeli zove se kljuc (en. key) ili primarni kljuc (en. primary key).

Baze podataka se sastoje od vise tabela za cije povezivanje se koristi kljucevi. Dodali smo drugu tabelu Porudzbine, koja sadrzi porudzbine kupaca. Svaki red u tabeli Porudzbine je jedna porudzbina jednog kupca. Zbog sifre kupca znamo cija je svaka poruzdbina. 

Primer: porudzbina broj 3, pripada kupcu pod sifrom 1, a to je Stevan Stevanic.

U relacionim bazama podataka, ovakva relacija zove se spoljni kljuc (en. foreign key). Kolona SifraKupca primarni je kljuc u tabeli Porudzbine. Ali ako postoji i u nekoj drugoj tabeli, tabela Porudzbine, onda je u toj tabeli spoljni kljuc. 

The concepts of relational databases:

• tables
• column
• lines
• value
• keys

Table - relational database consists of relations (relations between data). called tables. The table is a table of data.

Columns - the table contains a column in which are placed certain types of data. Columns of tables are sometimes called fields or attributes of the table.

Rows - each row in the table represents one customer. Because tabular format each row has the same attributes. Rows of tables are called records.

Values ​​- each row consists of a set of individual values ​​contained in the columns. Each value must have a data type specific to the column in which it is located.

Keys - there must be a way unequivocal identification of each customer. Each buyer assign a unique ID number. or the customerID.

The identity column in the table is called the key or primary key.

Databases consist of several tables for whose connection are used keys. We added a second table Orders, which contains customer orders. Each row in the table Orders is one orders of a single/one customer. Because of the customerID we know whose every order is.

For example, the order number 3, belongs to the customer under customerID 1, and that is Stevan Stevanic.

In relational databases, such relation is called an foreign key. Column customerID is the primary key in the table Orders. But if there is in another table, table Orders, then it is in that table foreign key.