I would like to make a quick MySQL 101 about numeric types in MySQL and especially explain the difference between the numeric type attributes and the maximum value that a numeric type can store.

Someone asked me yesterday why when he inserts a value in a table, the value 127 appears instead of the value 160 that he’s just inserted.
Ok, let me explain, consider this table :

What happens if you want to insert this row in the table :

sql > insert into product values (160, 554, "iPad mini");
Query OK, 1 row affected, 1 warning (0.01 sec)
sql > show warnings;
+---------+------+---------------------------------------------+
| Level   | Code | Message                                     |
+---------+------+---------------------------------------------+
| Warning | 1264 | Out of range value for column 'id' at row 1 | …

What’s the difference between INT(2) and INT(20) ? Not a lot. It’s about output formatting, which you’ll never encounter when talking with the server through an API (like you do from most app languages).

The confusion stems from the fact that with CHAR(n) and VARCHAR(n), the (n) signifies the length or maximum length of that field. But for INT, the range and storage size is specified using different data types: TINYINT, SMALLINT, MEDIUMINT, INT (aka INTEGER), BIGINT.

At Open Query we tend to pick on things like INT(2) when reviewing a client’s schema, because chances are that the developers/DBAs are working under a mistaken assumption and this could cause trouble somewhere – even if not in the exact spot where we pick on it. So it’s a case of pattern recognition.

A very practical example of this comes from a client I worked with last week. I first spotted some harmless ones, we talked about it, and then we hit …

In short, it really doesn’t matter.  After watching a MySQL web conference by Jay Pipes, I was gutted when I found out that they are actually exactly the same.  I know im not alone in thinking that it affected the size of the data field.  An unsigned int has the max value of 4294967295 no matter if its INT(1) or int(10) and will use 4 bytes of data.

So, what does the number in the brackets mean?  It pretty much comes down to display, its called the display-width.  The display width is a number from 1 to 255. You can set the display width if you want all of your integer values to “appear”.  If you enable zerofill on the row, the field will have a default value of 0 for int(1) and 0000000000 for int(10).

There are 5 main numeric data types, and you should …