Re: using alias in where clause

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

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