On 10/16/2012 6:29 PM, Bart Smissaert wrote:
Actually, it really is slow, made worse by the fact that there is not
one grouping
field (value in my example), but three. I am running your SQL now, concatenating
these 3 fields, but still running and looks will be a long time.
Will have to improve it with indexes and maybe avoiding the concatenation.
This would avoid concatenation:
update MyTable set Group_Marker = (
select count(*) from MyTable t1
where t1.ID <= MyTable.ID and not (
select (t2.Value1=t1.Value1 and t2.Value2=t1.Value2 and
t2.Value3=t1.Value3)
from MyTable t2 where t2.ID < t1.ID
order by t2.ID desc limit 1
)
);
The only index that would be helful is one on ID, which I suspect you
might already have.
--
Igor Tandetnik
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