Tables, rows and columns

Before we give the Library its first order, we must understand its structure well. Remember these three words - they will accompany you throughout your journey.

Table

A table is a single shelf - a collection of data of one kind. In our Library we will use several shelves:

• ksiazki

  - all books,

• autorzy

  - the creators of the books,

• czytelnicy

  - people enrolled in the Library,

• kategorie

  - thematic sections,

• wypozyczenia

  - who borrowed which book and when.

Row (record)

A row is a single scroll - one entry in a table. One row in

czytelnicy

describes one person:

| id | imie | nazwisko | miasto | |----|------|----------|--------| | 7 | Hypatia | of Alexandria | Alexandria |

Column (field)

A column is a single field describing all rows. In

czytelnicy

we have the columns

id

,

imie

,

nazwisko

,

miasto

. Each column has its type - e.g. text or number (more on types in the "Table Workshop" location).

Primary key (PRIMARY KEY)

Every shelf has its register of catalog numbers - a column that uniquely identifies each row. This is the primary key, most often the

id

column.

Thanks to the primary key:

• no two rows share the same catalog number,
• we can point to a specific scroll among thousands without mistake.

This is exactly the idea behind my Pinakes - a catalog that gives every scroll a unique number.