You should probably turn this into a UNION and put an index on each column:
SELECT f_tag_ch_y_bottom AS ftag FROM data_cst WHERE f_tag_ch_y_bottom = 'E-CD7' UNION ALL SELECT f_tag_ch_x_bottom AS ftag FROM data_cst WHERE f_tag_ch_x_bottom = 'E-CD7' UNION ALL SELECT f_tag_bottom_minor_axis AS ftag FROM data_cst WHERE f_tag_bottom_minor_axis = 'E-CD7' UNION ALL SELECT f_tag_bottom_major_axis AS ftag FROM data_cst WHERE f_tag_bottom_major_axis = 'E-CD7' UNION ALL SELECT f_tag_bottom FROM data_cst AS ftag WHERE f_tag_bottom = 'E-CD7' ; Doing this any other way will prevent index usage and a full table scan will be required. Is there a possibility of more than one column matching? How would you handle that? On Mon, Jan 25, 2016 at 6:16 PM, Larry Martell <larry.mart...@gmail.com> wrote: > 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? > > -- > MySQL General Mailing List > For list archives: http://lists.mysql.com/mysql > To unsubscribe: http://lists.mysql.com/mysql > > -- ----------------------------- Johnny Withers 601.209.4985 joh...@pixelated.net
