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Data type confusion: what is an int(11)?

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
tinyint 1
smallint 2
mediumint 3
int 4
bigint 8

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 |
+---------+

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Comment by Lucas Renan on November 1, 2009 at 5:58am
nice tip Sarah =]

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