func (this *builder) visitFrom(node *algebra.Subselect, group *algebra.Group) error { count, err := this.fastCount(node) if err != nil { return err } if count { this.maxParallelism = 1 } else if node.From() != nil { if this.where != nil || group != nil { this.limit = nil } _, err := node.From().Accept(this) if err != nil { return err } } else { // No FROM clause scan := plan.NewDummyScan() this.children = append(this.children, scan) this.maxParallelism = 1 } return nil }
func (this *builder) VisitSubselect(node *algebra.Subselect) (interface{}, error) { aggs, err := allAggregates(node, this.order) if err != nil { return nil, err } this.where = node.Where() group := node.Group() if group == nil && len(aggs) > 0 { group = algebra.NewGroup(nil, nil, nil) this.where = constrainAggregate(this.where, aggs) } this.children = make([]plan.Operator, 0, 16) // top-level children, executed sequentially this.subChildren = make([]plan.Operator, 0, 16) // sub-children, executed across data-parallel streams count, err := this.fastCount(node) if err != nil { return nil, err } if count { this.maxParallelism = 1 } else if node.From() != nil { if this.where != nil || group != nil { this.limit = nil } _, err := node.From().Accept(this) if err != nil { return nil, err } } else { // No FROM clause scan := plan.NewDummyScan() this.children = append(this.children, scan) this.maxParallelism = 1 } if this.coveringScan != nil { coverer := expression.NewCoverer(this.coveringScan.Covers()) err = this.cover.MapExpressions(coverer) if err != nil { return nil, err } if this.where != nil { this.where, err = coverer.Map(this.where) if err != nil { return nil, err } } } if node.Let() != nil { this.subChildren = append(this.subChildren, plan.NewLet(node.Let())) } if node.Where() != nil { this.subChildren = append(this.subChildren, plan.NewFilter(node.Where())) } if group != nil { this.visitGroup(group, aggs) } projection := node.Projection() this.subChildren = append(this.subChildren, plan.NewInitialProject(projection)) // Initial DISTINCT (parallel) if projection.Distinct() || this.distinct { this.subChildren = append(this.subChildren, plan.NewDistinct()) } if !this.delayProjection { // Perform the final projection if there is no subsequent ORDER BY this.subChildren = append(this.subChildren, plan.NewFinalProject()) } // Parallelize the subChildren this.children = append(this.children, plan.NewParallel(plan.NewSequence(this.subChildren...), this.maxParallelism)) // Final DISTINCT (serial) if projection.Distinct() || this.distinct { this.children = append(this.children, plan.NewDistinct()) } // Serialize the top-level children return plan.NewSequence(this.children...), nil }