Yep, you're right!
Perhaps an extra byte is automatically reserved, not only for a
null/not null status bit, but also for other internal use - eg; a
'row changed' bit, etc.
I did a quick test:
mysql> create table t2 (c1 varchar(255));
Query OK, 0 rows affected (0.00 sec)
mysql> insert into t2 values ('s');
Query OK, 1 row affected (0.00 sec)
And this gave table status of
Name: t2
Type: MyISAM
Row_format: Dynamic
Rows: 1
Avg_row_length: 20
Data_length: 20
Max_data_length: 4294967295
Index_length: 1024
Data_free: 0
Auto_increment: NULL
so obviously the avg_row_length includes extra bytes for mysql internal info.
Learn something every day!
-steve
At 1:03 PM +0100 1/15/03, you wrote:
>Steve,
>
>> I believe there is an extra byte for the 'null' flag; if you declare
>> this column to be NOT NULL, I'll bet the avg length will be 10.
>
>nice bet, but you lose <g>:
>
>mysql> DESCRIBE mynotnullisam;
>+-------+----------+------+-----+---------+-------+
>| Field | Type | Null | Key | Default | Extra |
>+-------+----------+------+-----+---------+-------+
>| col | char(10) | | | | |
>+-------+----------+------+-----+---------+-------+
>1 row in set (0.16 sec)
>
>mysql> SHOW TABLE STATUS LIKE 'mynotnullisam';
>+---------------+--------+------------+------+----------------+---------
>----+
>| Name | Type | Row_format | Rows | Avg_row_length |
>Data_length |
>+---------------+--------+------------+------+----------------+---------
>----+
>| mynotnullisam | MyISAM | Fixed | 3 | 11 |
>33 |
>+---------------+--------+------------+------+----------------+---------
>----+
>
--
+------------------------------------------------------------------------+
| Steve Edberg sbedberg@stripped |
| University of California, Davis (530)754-9127 |
| Programming/Database/SysAdmin http://pgfsun.ucdavis.edu/ |
+------------------------------------------------------------------------+
| SETI@Home: 1001 Work units on 23 oct 2002 |
| 3.152 years CPU time, 3.142 years SETI user... and STILL no aliens... |
+------------------------------------------------------------------------+
