Critical Description
KYLIN-1979 introduces a bug, which can cause extended column query returns wrong result if user defines more than one extended column metrics.
Example: let's define two extended columns 1. metricA(host=h1, extend=e1) 2. metricB(host=h2, extend=e2). "select h1, e1 ... group by h1,e1" correct. "select h1, e1, h2, e2 ... group by h1,e1, h2, e2" correct. "select h2, e2 ... group by h2, e2" wrong. (column e2 is empty)