Have you tried using a select case statement for ftag?
> On Jan 25, 2016, at 6:39 PM, Larry Martell <larry.mart...@gmail.com> wrote: > > On Mon, Jan 25, 2016 at 7:27 PM, Reindl Harald <h.rei...@thelounge.net> wrote: >> >> >> Am 26.01.2016 um 01:16 schrieb Larry Martell: >>> >>> I know I cannot use an alias in a where clause, but I am trying to >>> figure out how to achieve what I need. >>> >>> If I could have an alias in a where clause my sql would look like this: >>> >>> SELECT IFNULL(f_tag_bottom, >>> IFNULL(f_tag_bottom_major_axis, >>> IFNULL(f_tag_bottom_minor_axis, >>> IFNULL(f_tag_ch_x_bottom, >>> IFNULL(f_tag_ch_y_bottom, NULL))))) as ftag, >>> STDDEV(ch_x_top) >>> FROM data_cst >>> WHERE ftag = 'E-CD7' >>> GROUP BY wafer_id, lot_id >>> >>> But I can't use ftag in the where clause. I can't put it in a having >>> clause, as that would exclude the already aggregated rows and I want >>> to filter then before the aggregation. Anyone have any idea how I can >>> do this? >> >> >> why would you want to do that? >> it would make the where clause not be able to use proper indexes > > I do not know which of the 5 f_tag_* columns will be populated and I > need to filter on the one that is populated. > > -- > MySQL General Mailing List > For list archives: http://lists.mysql.com/mysql > To unsubscribe: http://lists.mysql.com/mysql > -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/mysql
