Re: sql query not use index
Date: Mon, 9 Mar 2009 12:49:44 -0700 (PDT)
On Mar 9, 1:11 pm, sydneypue..._at_yahoo.com wrote:
> Hello Guys,
> I was asked yesterday a project manager what sort of query will not
> use an index?
> What sort of index ? I asked
> say a varchar(256) ?
> A badly written regex. I responded.
> OK thanks.
Also any query involving a function call using the indexed column:
UPPER(colname) LOWER(colname) LTRIM(colname...) RTRIM(colname...)
ALSO a query against a nullable column which is not qualified by a where clause since B-Tree indexes don't index NULLs:
ALSO a query, with a WHERE clause, returning a large part of the table data, as the optimizer may decide a full table scan is more efficient (less work) than an index scan/table fetch by rowid for that much data:
> Now I am worried I have given a misleading or wrong response!
Incomplete, possibly, but not wrong.
> Can anyone help me out with a better answer?
David Fitzjarrell Received on Mon Mar 09 2009 - 14:49:44 CDT