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Re: using alias in where clause




2016/01/25 19:16 ... Larry Martell:
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)
....
Of course, this isn't your real problem, but you could use COALESCE instead of all those IFNULLs (and you don't need the last one): SELECT COALESCE(f_tag_bottom, f_tag_bottom_major_axis, f_tag_bottom_minor_axis, f_tag_ch_x_bottom, f_tag_ch_y_bottom) as ftag,
		STDDEV(ch_x_top)
	....

As Johnny Withers points out, you may repeat the expression in the WHERE-clause: WHERE COALESCE(f_tag_bottom, f_tag_bottom_major_axis, f_tag_bottom_minor_axis, f_tag_ch_x_bottom, f_tag_ch_y_bottom) = 'E-CD7'
If really only one of those is not NULL, it is equivalent to this:
'E-CD7' IN (f_tag_bottom, f_tag_bottom_major_axis, f_tag_bottom_minor_axis, f_tag_ch_x_bottom, f_tag_ch_y_bottom)

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