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Re: using alias in where clause




On Mon, Jan 25, 2016 at 8:01 PM, Rebecca Love <wacceber@xxxxxxxxx> wrote:
> Have you tried using a select case statement for ftag?

How would that help? Unless I'm missing something, I'd still have to
have a reference to the column alias in the where clause.


>> On Jan 25, 2016, at 6:39 PM, Larry Martell <larry.martell@xxxxxxxxx> wrote:
>>
>> On Mon, Jan 25, 2016 at 7:27 PM, Reindl Harald <h.reindl@xxxxxxxxxxxxx> 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.
>>
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