Incrementing a number then inserting it into the database problems

[cturner]

I am trying to increment the mainid number and am having no luck with it. I already have an autoincrement primary key number so the mainid number is different to that. At the moment it add two entries to the database but doesn't add the incremented number. Can someone please help me with this? Thanks in advance.

 

Here is my code:

$query05 = mysql_query("SELECT mainid FROM menu") or die ("Could not query because: ".mysql_error());
$row05 = mysql_fetch_assoc($query05);
$mainid = $row05['mainid'];
if ($mainid < 0) {
$insert06 = "INSERT INTO `menu` (`mainid`)
		VALUES ('$mainid + 1')";
f (mysql_query ($insert06)) {
print "Mainid added.";
} else {
print "<p>Could not add the entry because: <b>" . mysql_error() . "</b>. The query was $insert06.</p>";
}
} else {
$insert07 = "INSERT INTO `menu` (`mainid`)
		VALUES ('0')";
if (mysql_query ($insert07)) {
		print "0";
} else {
		print "<p>Could not add the entry because: <b>" . mysql_error() . "</b>. The query was $insert07.</p>";
}
}

[deadimp]

If you're just trying to increment the value of a field in a row, just use a simple update expression:

update `menu` set `mainid`=`mainid`+1 where `id`=?

where `id` is your primary index, and ? is the value of the id.

If you want to insert an item into a table with one more than the largest value:

insert into `menu` (`mainid`) values (max(`mainid`)+1)

The max() statement ought to work. If not, you could use a subquery or sometihng like that.

 

What's the point of this, though? You already have indexing with your auto increment field...

[fenway]

Careful with those updates, they're not thread-safe...