Hmm, this all sounds indeed like a terrific feature .. if it would work !
So, I decided to try it and just see what'll happen. I did the following
things:
* first I created a table:
mysql> create table autoIncrement (
-> id int(11) NOT NULL AUTO_INCREMENT,
-> thingie varchar(20) NOT NULL,
-> primary key(id, thingie)
-> );
Query OK, 0 rows affected (0.28 sec)
* inserted some values:
mysql> insert into autoIncrement (thingie) VALUES ("bla"),
-> ("boe"),
-> ("boer"),
-> ("en"),
-> ("joy");
Query OK, 5 rows affected (0.24 sec)
Records: 5 Duplicates: 0 Warnings: 0
did a select:
mysql> select * from autoIncrement;
+----+---------+
| id | thingie |
+----+---------+
| 1 | bla |
| 2 | boe |
| 3 | boer |
| 4 | en |
| 5 | joy |
+----+---------+
5 rows in set (0.04 sec)
Nothing seen from a counter for each value of thingie. I decided to insert a
value for thingie wich already existed, and to repeat the select:
mysql> insert into autoIncrement (thingie) values ("bla");
Query OK, 1 row affected (0.00 sec)
mysql> select * from autoIncrement;
+----+---------+
| id | thingie |
+----+---------+
| 1 | bla |
| 2 | boe |
| 3 | boer |
| 4 | en |
| 5 | joy |
| 6 | bla |
+----+---------+
6 rows in set (0.00 sec)
Again, no incrementing per value for the second element of the primary key.
Can you please tell me, Matthew, how did you do it? It sounds too good to be
true and so it seems to be, or isn't it?
Greetz,
Wouter
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-----Oorspronkelijk bericht-----
Van: Matthew Walker [mailto:[EMAIL PROTECTED]]
Verzonden: vrijdag 12 juli 2002 23:30
Aan: [EMAIL PROTECTED]
Onderwerp: Autoincrement in MultiColumn primary key?
filter: sql,query
I did some tests recently on a two column primary key, one of which was
an autoincrement column. It worked nicely, maintaining a separate
increment for every unique value in the second column. I was ecstatic,
as this was exactly what I need for some tables I'm designing.
However, today I tried to use the same idea in a three column primary
key, and it seems to be acting like a lone autoincrement column, instead
of how it acted with two columns.
What I want to know, is this: Is the two-column behavior an official
feature, or is it an unintended effect? I personally /love/ that
behavior, and think it should be a feature, but before I go further, I
need to know if I can count on it to hang around. And if it is a
feature, why it doesn't work in three column indexes.
Please CC the reply-to address in your responses.
Thanks for your time,
Matthew Walker
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