[数据库]Data type confusion: what is an int?
Over and over I see customers that don't understand what
int(11) really means. Their confusion is understandable. Many know what defining a
char(10) means (a fixed-sized character string that allows up to 10 characters). However, ints are different.First of all, there are 5 types of integer. They are all fixed size.
|Type||# of bytes|
As you can see from the chart, an
int is always 4 bytes. That can store signed numbers from -2 billion to +2 billion (and unsigned numbers 0 to 4B). So, what does it mean if you declare an
int(5)? It does not restrict the number of digits to 5... It may actually do nothing! The (5) part is a display width. It's only used if you use UNSIGNED and ZEROFILL with an integer type. Then the display of those numbers will be zero-padded on the left to 5 digits if they contain less than 5 digits. Example:
CREATE TABLE `foo` (
`bar` int(5) unsigned zerofill DEFAULT NULL
SELECT * FROM foo;+---------+
| bar |
| 00042 |
| 00101 |
| 9876543 |