MySQL按行号更新

Question

I need to update rows by their number(not AI ID, cause some of the rows may will be removed). How can I do this? I mean something like this:

UPDATE cars SET idx = value WHERE row_number = i

I would do this in a 'for' statement, and i is the integer of my statement. So I would update every row in the statement.

Sorry for my bad english, and thanks!

Answer 1

Here's a pure MySQL solution:

/*test data*/
create table foo (id int auto_increment primary key, a int);
insert into foo (a) values (10), (11), (12);

/*update statement*/
update foo
set a = 5
where id = (
   select id from (
      select id, @rownum:=@rownum + 1 as rownumber 
      from foo, (select @rownum:=0) vars order by id
   ) sq where rownumber = 2
);

Results in:

| ID |  A |
-----|----|--
|  1 | 10 |
|  2 |  5 |
|  3 | 12 |

Feel free to ask if you have any questions about this.

Also, note the order by id in there. It's important, cause in a database there is no first or last row. Without an order by clause theoretically there could be each time a different result.

You can also see it working live here in an sqlfiddle .

Answer 2

i don't know this about mysql but you can do this in php

$row_number=?   ;//the row no of mysql you want to change the id 
$id=? ;//the new id 
mysql_connect //do it yourself
$query="select 8 from tablename";  //the query
$result=mysql_query($qyery,$conn);
$count=0;
while($row=mysql_fetch_array($result)) // fetch each row one by one an put data in array $row
{
    $count++;     //increment count means the no of rows are incermented
    if($count==$rownumber)   //the row where you want to edit the id
    {
        $query1="update tablename set id='".$id."' where id=".$row["id"];  //new query on that particular row
        $result1=mysql_query($query1,$conn);
    }
}

this will work , just modify this code according to your use