I'm creating a messaging system (using PHP) and want to assign an ID number to each message (aside from each actual message having an unique ID number)...however, if someone replies to a message then i want to be able to give that message the same ID as the message being replied to...then of course I can disply them by time and show them in order.
So, if i give the field an auto_increment type is that able to be overwritten?
Meaning...each new message has auto value eg 1, 2, 3 etc but someone replies to number 2 so it's ID needs to also 2
Or is there a better way to do this?
Absolutely nothing prevents you from assigning any arbitrary value to an AUTO_INCREMENT
column. If necessary, the table counter will adjust accordingly.
However, you cannot set as AUTO_INCREMENT
a column that's not unique.
Honestly, I can't understand your design. A typical messaging system would look like this:
message_id in_reply_to
========== ===========
1 NULL
2 NULL
3 1
4 NULL
5 1
6 3
7 NULL
Duplicating IDs kind of beats the purpose of using IDs.
Update #1: OMG, it seems that it can actually be done under certain circumstances:
For MyISAM tables you can specify AUTO_INCREMENT on a secondary column in a multiple-column index. In this case, the generated value for the AUTO_INCREMENT column is calculated as MAX(auto_increment_column) + 1 WHERE prefix=given-prefix. This is useful when you want to put data into ordered groups.
http://dev.mysql.com/doc/refman/5.5/en/example-auto-increment.html
Update #2: For the records, I've just tested it and you can use duplicate auto-incremented IDs in InnoDB tables as well:
CREATE TABLE foo (
foo_id INT(10) NOT NULL DEFAULT '0',
bar_id INT(10) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (foo_id),
INDEX bar_id (bar_id)
)
ENGINE=InnoDB
不,auto_increment列不能多次出现。
I would keep each message ID unique - whether it is via auto increment or a uuid. Add an additional column to the message structure for thread_id - unique on creation, and then have all replies include this thread_id to link them together logically.
The way you would do this is have another column in your table called parent_id
or something of the sort.
The original message would have a parent_id of NULL.
Then, when anyone posts a reply to a message, then the original ID of the message goes into the parent_id
column of the new message. For instance:
id text parent_id created_at
============================================
1 'Lorem ipsum' null [time]
2 'Lorem ipsum' 1 [time]
3 'Lorem ipsum' 1 [time]
You could even go further and have the replies nested:
id text parent_id created_at
============================================
1 'Lorem ipsum' null [time]
2 'Lorem ipsum' 1 [time]
3 'Lorem ipsum' 2 [time]
In the latter case, you'd probably need some sort of recursive function to get all of the nested messages; the first way is simpler.
Best way to put unique id is; to add uniqid(rand()).
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