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Data types - choosing the right drawer

Every field of a shelf must know what kind of data it accepts. It is like drawers for scrolls: one for numbers, another for dates, another for long stories. In MySQL we call these drawers data types.

Numbers

INT - whole numbers, e.g. a year of publication, an identifier. Ideal for
```
rok_wydania
```
or
```
id
```
.
DECIMAL(p,s) - decimal numbers with exact precision.
```
p
```
is the total number of digits,
```
s
```
is the digits after the decimal point.
```
DECIMAL(8,2)
```
will store amounts like
```
29.99
```
- perfect for
```
cena
```
.

Text

VARCHAR(n) - text of variable length, up to
```
n
```
characters. For
```
tytul
```
we will use e.g.
```
VARCHAR(255)
```
, for
```
imie
```
-
```
VARCHAR(50)
```
.
TEXT - long texts without a strict limit, e.g. a book
```
opis
```
(description) or the content of a review.

Dates

DATE - a date alone, e.g.
```
2024-03-15
```
. Fits
```
data_wypozyczenia
```
,
```
data_zwrotu
```
.
DATETIME - a date together with a time, e.g.
```
2024-03-15 14:30:00
```
.

The golden rule

Match the type to the data! Numbers to INT, amounts to DECIMAL, short strings to VARCHAR, long descriptions to TEXT, dates to DATE. The wrong drawer means chaos in the Library - we do not keep numbers in a drawer meant for text, nor do we cram text into a drawer meant for numbers.

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