// filters walks the where clause of a select statement and returns a map with all series ids
// matching the where clause and any filter expression that should be applied to each
func (m *Measurement) filters(stmt *influxql.SelectStatement) (map[uint64]influxql.Expr, error) {
if stmt.Condition == nil || stmt.OnlyTimeDimensions() {
seriesIdsToExpr := make(map[uint64]influxql.Expr)
for _, id := range m.seriesIDs {
seriesIdsToExpr[id] = nil
}
return seriesIdsToExpr, nil
}
ids, seriesIdsToExpr, err := m.walkWhereForSeriesIds(stmt.Condition)
if err != nil {
return nil, err
}
// Ensure every id is in the map and replace literal true expressions with
// nil so the engine doesn't waste time evaluating them.
for _, id := range ids {
if expr, ok := seriesIdsToExpr[id]; !ok {
seriesIdsToExpr[id] = nil
} else if b, ok := expr.(*influxql.BooleanLiteral); ok && b.Val {
seriesIdsToExpr[id] = nil
}
}
return seriesIdsToExpr, nil
}
