Why I dont get an error setting larger INT datatype length in MySQL?

I'm a little bit开发者_如何学JAVA confused on datatypes length in MySql; I read the reference manual at http://dev.mysql.com/doc/refman/5.0/en/data-types.html and I know that when I write "INT(M)"...

M indicates the maximum display width for integer types. For floating-point and fixed-point types, M is the total number of digits that can be stored. For string types, M is the maximum length. The maximum permissible value of M depends on the data type.

Then, I added a column to my table with a field datatype like INT(10) [not unsigned] and I know that the maximum values are -2147483648 / 2147483647

However if I edit it to INT(11), MySQL permit me to set a larger length without any error although the length is out of the range; in this case, I'll get an error only when I set a value larger of 2147483647, why not before?

Thank You in advance,

Max

The M value doesn't affect the range of numbers you can store. You can save the same numbers in INT(1) as in INT(30). The number does only affect the ZEROFILL behavior.

mysql> CREATE TEMPORARY TABLE foobar(x INT(40) ZEROFILL);
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO foobar(x) VALUES (42);
Query OK, 1 row affected (0.00 sec)

mysql> SELECT * FROM foobar;
+------------------------------------------+
| x                                        |
+------------------------------------------+
| 0000000000000000000000000000000000000042 |
+------------------------------------------+
1 row in set (0.00 sec)

mysql>

I can only speculate, but my guess is that the display width setting just isn't smart enough to recognize the conflict. But seeing as the display width is just a recommendation for client programs anyway, I would argue it doesn't have to be.