Hi!
On Dec 19, mhansson@stripped wrote:
> ChangeSet@stripped, 2007-12-19 12:23:33+01:00, mhansson@stripped +5 -0
> Bug#33143: Incorrect ORDER BY for ROUND()/TRUNCATE() result
>
> The ROUND(X, D) function changes the scale of a result field X to D
> digits.
> When D is not constant, the binary encoding of a DECIMAL value, used
> in filesort cannot guarantee proper ordering.
> Fixed by using the scale of X (as opposed to that of any expression
> containong ROUND) in the temporary table, and changing number of
> digits only when retreiving sorted values from the temporary table.
I don't think it's conceptually correct.
That is, you found the problem corectly, but I believe an Item is not
allowed to change the metadata after fix_fields. Item_func_round is just
wrong, breaking the api. Adding a workaround to the hierarchy root Item
is not a proper fix then, the fix should be to fix Item_func_round.
Item_func_round only messes with metadata to have ::val_str() to
generate the correct number of digits. There could be other ways to
achieve the same. E.g.:
Item_func_round::val_str(String *s)
{
uint8 old_dec=decimals;
String *res=Item_func_num1::val_str(s);
decimals=old_dec;
return res;
}
or introducing runtime_decimals, or whatever. Keeping implementation
problems of the Item_func_round in the Item_func_round.
Regards / Mit vielen Grüssen,
Sergei
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