// WhereFields returns a list of non-"time" fields in the WHERE section of stmt.
func (m *Measurement) WhereFields(stmt *influxql.SelectStatement) []string {
set := newStringSet()
for _, name := range stmt.NamesInWhere() {
if name != "time" && m.HasField(name) {
set.add(name)
}
}
return set.list()
}