MySQL的插入和更新表最大3

Question

I have a php script that logs inputs from a form into a mysql database table. I'm looking for a way to insert this data untill 3 rows are created, after which it has to update the existing rows so that the first one updates to the new input, the second one to the former first input and the third one to the former second input.

Table:

CREATE TABLE IF NOT EXISTS inputlog (
  id int(11) NOT NULL auto_increment,
  userid int(11) NOT NULL default '0',
  name text,
  value text,
  PRIMARY KEY (id)
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1;`

For the first three rows i use:

insert into inputlog (userid,name,value) values('$userid','$name','$value')

After that is has to become:

update inputlog set value = '$value' where userid = '$userid' and name = '$name'

where it has to update all the successive rows.

How can i accomplish this?

Answer 1

Too long for comments, so...

Looks like you want to have only 3 rows in your table because you want the data to be sorted by the id. So id=1 will be the latest value, then id=2 and finally id=3.

In short, do not do that, the id field can be any value. Do not code for that. The danger is if you use the id in another table as a foreign key, you will loose referential integrity. What I propose is:

• Add an timestamp column for each row.
• Every time you insert a new value, set the timestamp column to NOW()
• When selecting, sort on the timestamp and limit to 3 results

If you MUST have only 3 rows, you can then delete the row except for the 3 most recent timestamps.

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But... if you must do that...

• perform a SELECT with the first 2 lines
• truncate the table (delete all rows)
• insert the new line, then the 2 stored lines

You will then ahve your 3 rows in the order you want. But without seeing the entire reasoning for your application, my "spider sense" tells me you will hit a wall later on...

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And check the comments for other things to worry about.