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:

Column (field)

A column is a single field describing all rows. czytelnicy has, among others, the columns id, imie, nazwisko and miasto (the full list is on the map of the shelves). Where a row and a column meet lies a single value - e.g. the first name of one particular person. 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.

My Pinakes followed the same idea: I described every work (author, title, opening words) so that it could never be confused with another. A database goes one step further and gives every row a unique number.