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select.go
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select.go
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// Copyright 2016, Google Inc. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package planbuilder
import (
"errors"
"fmt"
"github.com/youtube/vitess/go/vt/sqlparser"
"github.com/youtube/vitess/go/vt/vtgate/engine"
"github.com/youtube/vitess/go/vt/vtgate/vindexes"
)
// buildSelectPlan is the new function to build a Select plan.
func buildSelectPlan(sel *sqlparser.Select, vschema VSchema) (primitive engine.Primitive, err error) {
bindvars := sqlparser.GetBindvars(sel)
builder, err := processSelect(sel, vschema, nil)
if err != nil {
return nil, err
}
jt := newJointab(bindvars)
err = builder.Wireup(builder, jt)
if err != nil {
return nil, err
}
return builder.Primitive(), nil
}
// processSelect builds a primitive tree for the given query or subquery.
func processSelect(sel *sqlparser.Select, vschema VSchema, outer builder) (builder, error) {
bldr, err := processTableExprs(sel.From, vschema)
if err != nil {
return nil, err
}
if outer != nil {
bldr.Symtab().Outer = outer.Symtab()
}
if sel.Where != nil {
err = pushFilter(sel.Where.Expr, bldr, sqlparser.WhereStr)
if err != nil {
return nil, err
}
}
err = pushSelectExprs(sel, bldr)
if err != nil {
return nil, err
}
if sel.Having != nil {
err = pushFilter(sel.Having.Expr, bldr, sqlparser.HavingStr)
if err != nil {
return nil, err
}
}
err = pushOrderBy(sel.OrderBy, bldr)
if err != nil {
return nil, err
}
err = pushLimit(sel.Limit, bldr)
if err != nil {
return nil, err
}
bldr.PushMisc(sel)
return bldr, nil
}
// pushFilter identifies the target route for the specified bool expr,
// pushes it down, and updates the route info if the new constraint improves
// the primitive. This function can push to a WHERE or HAVING clause.
func pushFilter(boolExpr sqlparser.Expr, bldr builder, whereType string) error {
filters := splitAndExpression(nil, boolExpr)
reorderBySubquery(filters)
for _, filter := range filters {
rb, err := findRoute(filter, bldr)
if err != nil {
return err
}
err = rb.PushFilter(filter, whereType)
if err != nil {
return err
}
}
return nil
}
// reorderBySubquery reorders the filters by pushing subqueries
// to the end. This allows the non-subquery filters to be
// pushed first because they can potentially improve the routing
// plan, which can later allow a filter containing a subquery
// to successfully merge with the corresponding route.
func reorderBySubquery(filters []sqlparser.Expr) {
max := len(filters)
for i := 0; i < max; i++ {
if !hasSubquery(filters[i]) {
continue
}
saved := filters[i]
for j := i; j < len(filters)-1; j++ {
filters[j] = filters[j+1]
}
filters[len(filters)-1] = saved
max--
}
}
// pushSelectExprs identifies the target route for the
// select expressions and pushes them down.
func pushSelectExprs(sel *sqlparser.Select, bldr builder) error {
err := checkAggregates(sel, bldr)
if err != nil {
return err
}
if sel.Distinct != "" {
// We know it's a route, but this may change
// in the distant future.
bldr.(*route).MakeDistinct()
}
colsyms, err := pushSelectRoutes(sel.SelectExprs, bldr)
if err != nil {
return err
}
bldr.Symtab().Colsyms = colsyms
err = pushGroupBy(sel.GroupBy, bldr)
if err != nil {
return err
}
return nil
}
// checkAggregates returns an error if the select statement
// has aggregates that cannot be pushed down due to a complex
// plan.
func checkAggregates(sel *sqlparser.Select, bldr builder) error {
hasAggregates := false
if sel.Distinct != "" {
hasAggregates = true
} else {
_ = sqlparser.Walk(func(node sqlparser.SQLNode) (kontinue bool, err error) {
switch node := node.(type) {
case *sqlparser.FuncExpr:
if node.IsAggregate() {
hasAggregates = true
return false, errors.New("dummy")
}
case *sqlparser.GroupConcatExpr:
hasAggregates = true
return false, errors.New("dummy")
}
return true, nil
}, sel.SelectExprs)
}
if !hasAggregates {
return nil
}
// Check if we can allow aggregates.
rb, ok := bldr.(*route)
if !ok {
return errors.New("unsupported: complex join with aggregates")
}
if rb.IsSingle() {
return nil
}
// It's a scatter rb. We can allow aggregates if there is a unique
// vindex in the select list.
for _, selectExpr := range sel.SelectExprs {
switch selectExpr := selectExpr.(type) {
case *sqlparser.NonStarExpr:
vindex := bldr.Symtab().Vindex(selectExpr.Expr, rb, true)
if vindex != nil && vindexes.IsUnique(vindex) {
return nil
}
}
}
return errors.New("unsupported: scatter with aggregates")
}
// pusheSelectRoutes is a convenience function that pushes all the select
// expressions and returns the list of colsyms generated for it.
func pushSelectRoutes(selectExprs sqlparser.SelectExprs, bldr builder) ([]*colsym, error) {
colsyms := make([]*colsym, len(selectExprs))
for i, node := range selectExprs {
switch node := node.(type) {
case *sqlparser.NonStarExpr:
rb, err := findRoute(node.Expr, bldr)
if err != nil {
return nil, err
}
colsyms[i], _, err = bldr.PushSelect(node, rb)
if err != nil {
return nil, err
}
case *sqlparser.StarExpr:
// We'll allow select * for simple routes.
rb, ok := bldr.(*route)
if !ok {
return nil, errors.New("unsupported: '*' expression in complex join")
}
// Validate keyspace reference if any.
if !node.TableName.IsEmpty() {
if qual := node.TableName.Qualifier; !qual.IsEmpty() {
if qual.String() != rb.ERoute.Keyspace.Name {
return nil, fmt.Errorf("cannot resolve %s to keyspace %s", sqlparser.String(node), rb.ERoute.Keyspace.Name)
}
}
}
// We can push without validating the reference because
// MySQL will fail if it's invalid.
colsyms[i] = rb.PushStar(node)
case sqlparser.Nextval:
// For now, this is only supported as an implicit feature
// for auto_inc in inserts.
return nil, errors.New("unsupported: NEXT VALUES construct")
}
}
return colsyms, nil
}