This change ensures that if there are any fields in the WHERE clause of
an aggregate that are different from the fields in the SELECT clause,
that the cursors also decode those fields. Otherwise WHERE clauses of
the form 'SELECT f(w) FROM x WHERE y=z' will return incorrect results
Fixes issue #4701.
This commit refactors the tsdb query engine to use separate aggregate
and raw execution paths, encapsulates cursor functionality, and removes
the TagSetCursor from the aggregate path. By removing the TagSetCursor,
we can pass sets of unordered values to the map functions and bypass
the `container/heap` entirely.
Philip O'Toole
liang@qiniu.com
Philip O'Toole
Nathaniel Cook
mengjinglei
Cory LaNou
Ben Johnson