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// Copyright 2016 PingCAP, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
// // Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
package core
import (
"context"
"github.com/pingcap/parser/ast"
"github.com/pingcap/parser/mysql"
"github.com/pingcap/tidb/expression"
"github.com/pingcap/tidb/kv"
"github.com/pingcap/tidb/sessionctx"
"github.com/pingcap/tidb/types"
)
type ppdSolver struct{}
func (s *ppdSolver) optimize(ctx context.Context, lp LogicalPlan) (LogicalPlan, error) {
_, p := lp.PredicatePushDown(nil)
return p, nil
}
func addSelection(p LogicalPlan, child LogicalPlan, conditions []expression.Expression, chIdx int) {
if len(conditions) == 0 {
p.Children()[chIdx] = child
return
}
conditions = expression.PropagateConstant(p.SCtx(), conditions)
// Return table dual when filter is constant false or null.
dual := Conds2TableDual(child, conditions)
if dual != nil {
p.Children()[chIdx] = dual
return
}
selection := LogicalSelection{Conditions: conditions}.Init(p.SCtx(), p.SelectBlockOffset())
selection.SetChildren(child)
p.Children()[chIdx] = selection
}
// PredicatePushDown implements LogicalPlan interface.
func (p *baseLogicalPlan) PredicatePushDown(predicates []expression.Expression) ([]expression.Expression, LogicalPlan) {
if len(p.children) == 0 {
return predicates, p.self
}
child := p.children[0]
rest, newChild := child.PredicatePushDown(predicates)
addSelection(p.self, newChild, rest, 0)
return nil, p.self
}
func splitSetGetVarFunc(filters []expression.Expression) ([]expression.Expression, []expression.Expression) {
canBePushDown := make([]expression.Expression, 0, len(filters))
canNotBePushDown := make([]expression.Expression, 0, len(filters))
for _, expr := range filters {
if expression.HasGetSetVarFunc(expr) {
canNotBePushDown = append(canNotBePushDown, expr)
} else {
canBePushDown = append(canBePushDown, expr)
}
}
return canBePushDown, canNotBePushDown
}
// PredicatePushDown implements LogicalPlan PredicatePushDown interface.
func (p *LogicalSelection) PredicatePushDown(predicates []expression.Expression) ([]expression.Expression, LogicalPlan) {
canBePushDown, canNotBePushDown := splitSetGetVarFunc(p.Conditions)
retConditions, child := p.children[0].PredicatePushDown(append(canBePushDown, predicates...))
retConditions = append(retConditions, canNotBePushDown...)
if len(retConditions) > 0 {
p.Conditions = expression.PropagateConstant(p.ctx, retConditions)
// Return table dual when filter is constant false or null.
dual := Conds2TableDual(p, p.Conditions)
if dual != nil {
return nil, dual
}
return nil, p
}
return nil, child
}
// PredicatePushDown implements LogicalPlan PredicatePushDown interface.
func (p *LogicalUnionScan) PredicatePushDown(predicates []expression.Expression) ([]expression.Expression, LogicalPlan) {
retainedPredicates, _ := p.children[0].PredicatePushDown(predicates)
p.conditions = make([]expression.Expression, 0, len(predicates))
p.conditions = append(p.conditions, predicates...)
// The conditions in UnionScan is only used for added rows, so parent Selection should not be removed.
return retainedPredicates, p
}
// PredicatePushDown implements LogicalPlan PredicatePushDown interface.
func (ds *DataSource) PredicatePushDown(predicates []expression.Expression) ([]expression.Expression, LogicalPlan) {
ds.allConds = predicates
ds.pushedDownConds, predicates = expression.PushDownExprs(ds.ctx.GetSessionVars().StmtCtx, predicates, ds.ctx.GetClient(), kv.UnSpecified)
return predicates, ds
}
// PredicatePushDown implements LogicalPlan PredicatePushDown interface.
func (p *LogicalTableDual) PredicatePushDown(predicates []expression.Expression) ([]expression.Expression, LogicalPlan) {
return predicates, p
}
// PredicatePushDown implements LogicalPlan PredicatePushDown interface.
func (p *LogicalJoin) PredicatePushDown(predicates []expression.Expression) (ret []expression.Expression, retPlan LogicalPlan) {
simplifyOuterJoin(p, predicates)
var equalCond []*expression.ScalarFunction
var leftPushCond, rightPushCond, otherCond, leftCond, rightCond []expression.Expression
switch p.JoinType {
case LeftOuterJoin, LeftOuterSemiJoin, AntiLeftOuterSemiJoin:
predicates = p.outerJoinPropConst(predicates)
dual := Conds2TableDual(p, predicates)
if dual != nil {
return ret, dual
}
// Handle where conditions
predicates = expression.ExtractFiltersFromDNFs(p.ctx, predicates)
// Only derive left where condition, because right where condition cannot be pushed down
equalCond, leftPushCond, rightPushCond, otherCond = p.extractOnCondition(predicates, true, false)
leftCond = leftPushCond
// Handle join conditions, only derive right join condition, because left join condition cannot be pushed down
_, derivedRightJoinCond := DeriveOtherConditions(p, false, true)
rightCond = append(p.RightConditions, derivedRightJoinCond...)
p.RightConditions = nil
ret = append(expression.ScalarFuncs2Exprs(equalCond), otherCond...)
ret = append(ret, rightPushCond...)
case RightOuterJoin:
predicates = p.outerJoinPropConst(predicates)
dual := Conds2TableDual(p, predicates)
if dual != nil {
return ret, dual
}
// Handle where conditions
predicates = expression.ExtractFiltersFromDNFs(p.ctx, predicates)
// Only derive right where condition, because left where condition cannot be pushed down
equalCond, leftPushCond, rightPushCond, otherCond = p.extractOnCondition(predicates, false, true)
rightCond = rightPushCond
// Handle join conditions, only derive left join condition, because right join condition cannot be pushed down
derivedLeftJoinCond, _ := DeriveOtherConditions(p, true, false)
leftCond = append(p.LeftConditions, derivedLeftJoinCond...)
p.LeftConditions = nil
ret = append(expression.ScalarFuncs2Exprs(equalCond), otherCond...)
ret = append(ret, leftPushCond...)
case SemiJoin, InnerJoin:
tempCond := make([]expression.Expression, 0, len(p.LeftConditions)+len(p.RightConditions)+len(p.EqualConditions)+len(p.OtherConditions)+len(predicates))
tempCond = append(tempCond, p.LeftConditions...)
tempCond = append(tempCond, p.RightConditions...)
tempCond = append(tempCond, expression.ScalarFuncs2Exprs(p.EqualConditions)...)
tempCond = append(tempCond, p.OtherConditions...)
tempCond = append(tempCond, predicates...)
tempCond = expression.ExtractFiltersFromDNFs(p.ctx, tempCond)
tempCond = expression.PropagateConstant(p.ctx, tempCond)
// Return table dual when filter is constant false or null.
dual := Conds2TableDual(p, tempCond)
if dual != nil {
return ret, dual
}
equalCond, leftPushCond, rightPushCond, otherCond = p.extractOnCondition(tempCond, true, true)
p.LeftConditions = nil
p.RightConditions = nil
p.EqualConditions = equalCond
p.OtherConditions = otherCond
leftCond = leftPushCond
rightCond = rightPushCond
case AntiSemiJoin:
predicates = expression.PropagateConstant(p.ctx, predicates)
// Return table dual when filter is constant false or null.
dual := Conds2TableDual(p, predicates)
if dual != nil {
return ret, dual
}
// `predicates` should only contain left conditions or constant filters.
_, leftPushCond, rightPushCond, _ = p.extractOnCondition(predicates, true, true)
// Do not derive `is not null` for anti join, since it may cause wrong results.
// For example:
// `select * from t t1 where t1.a not in (select b from t t2)` does not imply `t2.b is not null`,
// `select * from t t1 where t1.a not in (select a from t t2 where t1.b = t2.b` does not imply `t1.b is not null`,
// `select * from t t1 where not exists (select * from t t2 where t2.a = t1.a)` does not imply `t1.a is not null`,
leftCond = leftPushCond
rightCond = append(p.RightConditions, rightPushCond...)
p.RightConditions = nil
}
leftCond = expression.RemoveDupExprs(p.ctx, leftCond)
rightCond = expression.RemoveDupExprs(p.ctx, rightCond)
leftRet, lCh := p.children[0].PredicatePushDown(leftCond)
rightRet, rCh := p.children[1].PredicatePushDown(rightCond)
addSelection(p, lCh, leftRet, 0)
addSelection(p, rCh, rightRet, 1)
p.updateEQCond()
p.mergeSchema()
buildKeyInfo(p)
return ret, p.self
}
// updateEQCond will extract the arguments of a equal condition that connect two expressions.
func (p *LogicalJoin) updateEQCond() {
lChild, rChild := p.children[0], p.children[1]
var lKeys, rKeys []expression.Expression
for i := len(p.OtherConditions) - 1; i >= 0; i-- {
need2Remove := false
if eqCond, ok := p.OtherConditions[i].(*expression.ScalarFunction); ok && eqCond.FuncName.L == ast.EQ {
// If it is a column equal condition converted from `[not] in (subq)`, do not move it
// to EqualConditions, and keep it in OtherConditions. Reference comments in `extractOnCondition`
// for detailed reasons.
if expression.IsEQCondFromIn(eqCond) {
continue
}
lExpr, rExpr := eqCond.GetArgs()[0], eqCond.GetArgs()[1]
if expression.ExprFromSchema(lExpr, lChild.Schema()) && expression.ExprFromSchema(rExpr, rChild.Schema()) {
lKeys = append(lKeys, lExpr)
rKeys = append(rKeys, rExpr)
need2Remove = true
} else if expression.ExprFromSchema(lExpr, rChild.Schema()) && expression.ExprFromSchema(rExpr, lChild.Schema()) {
lKeys = append(lKeys, rExpr)
rKeys = append(rKeys, lExpr)
need2Remove = true
}
}
if need2Remove {
p.OtherConditions = append(p.OtherConditions[:i], p.OtherConditions[i+1:]...)
}
}
if len(lKeys) > 0 {
needLProj, needRProj := false, false
for i := range lKeys {
_, lOk := lKeys[i].(*expression.Column)
_, rOk := rKeys[i].(*expression.Column)
needLProj = needLProj || !lOk
needRProj = needRProj || !rOk
}
var lProj, rProj *LogicalProjection
if needLProj {
lProj = p.getProj(0)
}
if needRProj {
rProj = p.getProj(1)
}
for i := range lKeys {
lKey, rKey := lKeys[i], rKeys[i]
if lProj != nil {
lKey = lProj.appendExpr(lKey)
}
if rProj != nil {
rKey = rProj.appendExpr(rKey)
}
eqCond := expression.NewFunctionInternal(p.ctx, ast.EQ, types.NewFieldType(mysql.TypeTiny), lKey, rKey)
p.EqualConditions = append(p.EqualConditions, eqCond.(*expression.ScalarFunction))
}
}
}
func (p *LogicalProjection) appendExpr(expr expression.Expression) *expression.Column {
if col, ok := expr.(*expression.Column); ok {
return col
}
expr = expression.ColumnSubstitute(expr, p.schema, p.Exprs)
p.Exprs = append(p.Exprs, expr)
col := &expression.Column{
UniqueID: p.ctx.GetSessionVars().AllocPlanColumnID(),
RetType: expr.GetType(),
}
col.SetCoercibility(expr.Coercibility())
p.schema.Append(col)
return col
}
func (p *LogicalJoin) getProj(idx int) *LogicalProjection {
child := p.children[idx]
proj, ok := child.(*LogicalProjection)
if ok {
return proj
}
proj = LogicalProjection{Exprs: make([]expression.Expression, 0, child.Schema().Len())}.Init(p.ctx, child.SelectBlockOffset())
for _, col := range child.Schema().Columns {
proj.Exprs = append(proj.Exprs, col)
}
proj.SetSchema(child.Schema().Clone())
proj.SetChildren(child)
p.children[idx] = proj
return proj
}
// simplifyOuterJoin transforms "LeftOuterJoin/RightOuterJoin" to "InnerJoin" if possible.
func simplifyOuterJoin(p *LogicalJoin, predicates []expression.Expression) {
if p.JoinType != LeftOuterJoin && p.JoinType != RightOuterJoin && p.JoinType != InnerJoin {
return
}
innerTable := p.children[0]
outerTable := p.children[1]
if p.JoinType == LeftOuterJoin {
innerTable, outerTable = outerTable, innerTable
}
// first simplify embedded outer join.
if innerPlan, ok := innerTable.(*LogicalJoin); ok {
simplifyOuterJoin(innerPlan, predicates)
}
if outerPlan, ok := outerTable.(*LogicalJoin); ok {
simplifyOuterJoin(outerPlan, predicates)
}
if p.JoinType == InnerJoin {
return
}
// then simplify embedding outer join.
canBeSimplified := false
for _, expr := range predicates {
// avoid the case where the expr only refers to the schema of outerTable
if expression.ExprFromSchema(expr, outerTable.Schema()) {
continue
}
isOk := isNullRejected(p.ctx, innerTable.Schema(), expr)
if isOk {
canBeSimplified = true
break
}
}
if canBeSimplified {
p.JoinType = InnerJoin
}
}
// isNullRejected check whether a condition is null-rejected
// A condition would be null-rejected in one of following cases:
// If it is a predicate containing a reference to an inner table that evaluates to UNKNOWN or FALSE when one of its arguments is NULL.
// If it is a conjunction containing a null-rejected condition as a conjunct.
// If it is a disjunction of null-rejected conditions.
func isNullRejected(ctx sessionctx.Context, schema *expression.Schema, expr expression.Expression) bool {
expr = expression.PushDownNot(ctx, expr)
sc := ctx.GetSessionVars().StmtCtx
sc.InNullRejectCheck = true
result := expression.EvaluateExprWithNull(ctx, schema, expr)
sc.InNullRejectCheck = false
x, ok := result.(*expression.Constant)
if !ok {
return false
}
if x.Value.IsNull() {
return true
} else if isTrue, err := x.Value.ToBool(sc); err == nil && isTrue == 0 {
return true
}
return false
}
// PredicatePushDown implements LogicalPlan PredicatePushDown interface.
func (p *LogicalProjection) PredicatePushDown(predicates []expression.Expression) (ret []expression.Expression, retPlan LogicalPlan) {
canBePushed := make([]expression.Expression, 0, len(predicates))
canNotBePushed := make([]expression.Expression, 0, len(predicates))
for _, expr := range p.Exprs {
if expression.HasAssignSetVarFunc(expr) {
_, child := p.baseLogicalPlan.PredicatePushDown(nil)
return predicates, child
}
}
for _, cond := range predicates {
newFilter := expression.ColumnSubstitute(cond, p.Schema(), p.Exprs)
if !expression.HasGetSetVarFunc(newFilter) {
canBePushed = append(canBePushed, expression.ColumnSubstitute(cond, p.Schema(), p.Exprs))
} else {
canNotBePushed = append(canNotBePushed, cond)
}
}
remained, child := p.baseLogicalPlan.PredicatePushDown(canBePushed)
return append(remained, canNotBePushed...), child
}
// PredicatePushDown implements LogicalPlan PredicatePushDown interface.
func (p *LogicalUnionAll) PredicatePushDown(predicates []expression.Expression) (ret []expression.Expression, retPlan LogicalPlan) {
for i, proj := range p.children {
newExprs := make([]expression.Expression, 0, len(predicates))
newExprs = append(newExprs, predicates...)
retCond, newChild := proj.PredicatePushDown(newExprs)
addSelection(p, newChild, retCond, i)
}
return nil, p
}
// PredicatePushDown implements LogicalPlan PredicatePushDown interface.
func (la *LogicalAggregation) PredicatePushDown(predicates []expression.Expression) (ret []expression.Expression, retPlan LogicalPlan) {
var condsToPush []expression.Expression
exprsOriginal := make([]expression.Expression, 0, len(la.AggFuncs))
for _, fun := range la.AggFuncs {
exprsOriginal = append(exprsOriginal, fun.Args[0])
}
groupByColumns := expression.NewSchema(la.groupByCols...)
for _, cond := range predicates {
switch cond.(type) {
case *expression.Constant:
condsToPush = append(condsToPush, cond)
// Consider SQL list "select sum(b) from t group by a having 1=0". "1=0" is a constant predicate which should be
// retained and pushed down at the same time. Because we will get a wrong query result that contains one column
// with value 0 rather than an empty query result.
ret = append(ret, cond)
case *expression.ScalarFunction:
extractedCols := expression.ExtractColumns(cond)
ok := true
for _, col := range extractedCols {
if !groupByColumns.Contains(col) {
ok = false
break
}
}
if ok {
newFunc := expression.ColumnSubstitute(cond, la.Schema(), exprsOriginal)
condsToPush = append(condsToPush, newFunc)
} else {
ret = append(ret, cond)
}
default:
ret = append(ret, cond)
}
}
la.baseLogicalPlan.PredicatePushDown(condsToPush)
return ret, la
}
// PredicatePushDown implements LogicalPlan PredicatePushDown interface.
func (p *LogicalLimit) PredicatePushDown(predicates []expression.Expression) ([]expression.Expression, LogicalPlan) {
// Limit forbids any condition to push down.
p.baseLogicalPlan.PredicatePushDown(nil)
return predicates, p
}
// PredicatePushDown implements LogicalPlan PredicatePushDown interface.
func (p *LogicalMaxOneRow) PredicatePushDown(predicates []expression.Expression) ([]expression.Expression, LogicalPlan) {
// MaxOneRow forbids any condition to push down.
p.baseLogicalPlan.PredicatePushDown(nil)
return predicates, p
}
// DeriveOtherConditions given a LogicalJoin, check the OtherConditions to see if we can derive more
// conditions for left/right child pushdown.
func DeriveOtherConditions(p *LogicalJoin, deriveLeft bool, deriveRight bool) (leftCond []expression.Expression,
rightCond []expression.Expression) {
leftPlan, rightPlan := p.children[0], p.children[1]
isOuterSemi := (p.JoinType == LeftOuterSemiJoin) || (p.JoinType == AntiLeftOuterSemiJoin)
for _, expr := range p.OtherConditions {
if deriveLeft {
leftRelaxedCond := expression.DeriveRelaxedFiltersFromDNF(expr, leftPlan.Schema())
if leftRelaxedCond != nil {
leftCond = append(leftCond, leftRelaxedCond)
}
notNullExpr := deriveNotNullExpr(expr, leftPlan.Schema())
if notNullExpr != nil {
leftCond = append(leftCond, notNullExpr)
}
}
if deriveRight {
rightRelaxedCond := expression.DeriveRelaxedFiltersFromDNF(expr, rightPlan.Schema())
if rightRelaxedCond != nil {
rightCond = append(rightCond, rightRelaxedCond)
}
// For LeftOuterSemiJoin and AntiLeftOuterSemiJoin, we can actually generate
// `col is not null` according to expressions in `OtherConditions` now, but we
// are putting column equal condition converted from `in (subq)` into
// `OtherConditions`(@sa https://github.com/pingcap/tidb/pull/9051), then it would
// cause wrong results, so we disable this optimization for outer semi joins now.
// TODO enable this optimization for outer semi joins later by checking whether
// condition in `OtherConditions` is converted from `in (subq)`.
if isOuterSemi {
continue
}
notNullExpr := deriveNotNullExpr(expr, rightPlan.Schema())
if notNullExpr != nil {
rightCond = append(rightCond, notNullExpr)
}
}
}
return
}
// deriveNotNullExpr generates a new expression `not(isnull(col))` given `col1 op col2`,
// in which `col` is in specified schema. Caller guarantees that only one of `col1` or
// `col2` is in schema.
func deriveNotNullExpr(expr expression.Expression, schema *expression.Schema) expression.Expression {
binop, ok := expr.(*expression.ScalarFunction)
if !ok || len(binop.GetArgs()) != 2 {
return nil
}
ctx := binop.GetCtx()
arg0, lOK := binop.GetArgs()[0].(*expression.Column)
arg1, rOK := binop.GetArgs()[1].(*expression.Column)
if !lOK || !rOK {
return nil
}
childCol := schema.RetrieveColumn(arg0)
if childCol == nil {
childCol = schema.RetrieveColumn(arg1)
}
if isNullRejected(ctx, schema, expr) && !mysql.HasNotNullFlag(childCol.RetType.Flag) {
return expression.BuildNotNullExpr(ctx, childCol)
}
return nil
}
// Conds2TableDual builds a LogicalTableDual if cond is constant false or null.
func Conds2TableDual(p LogicalPlan, conds []expression.Expression) LogicalPlan {
if len(conds) != 1 {
return nil
}
con, ok := conds[0].(*expression.Constant)
if !ok {
return nil
}
sc := p.SCtx().GetSessionVars().StmtCtx
if expression.ContainMutableConst(p.SCtx(), []expression.Expression{con}) {
return nil
}
if isTrue, err := con.Value.ToBool(sc); (err == nil && isTrue == 0) || con.Value.IsNull() {
dual := LogicalTableDual{}.Init(p.SCtx(), p.SelectBlockOffset())
dual.SetSchema(p.Schema())
return dual
}
return nil
}
// outerJoinPropConst propagates constant equal and column equal conditions over outer join.
func (p *LogicalJoin) outerJoinPropConst(predicates []expression.Expression) []expression.Expression {
outerTable := p.children[0]
innerTable := p.children[1]
if p.JoinType == RightOuterJoin {
innerTable, outerTable = outerTable, innerTable
}
lenJoinConds := len(p.EqualConditions) + len(p.LeftConditions) + len(p.RightConditions) + len(p.OtherConditions)
joinConds := make([]expression.Expression, 0, lenJoinConds)
for _, equalCond := range p.EqualConditions {
joinConds = append(joinConds, equalCond)
}
joinConds = append(joinConds, p.LeftConditions...)
joinConds = append(joinConds, p.RightConditions...)
joinConds = append(joinConds, p.OtherConditions...)
p.EqualConditions = nil
p.LeftConditions = nil
p.RightConditions = nil
p.OtherConditions = nil
nullSensitive := p.JoinType == AntiLeftOuterSemiJoin || p.JoinType == LeftOuterSemiJoin
joinConds, predicates = expression.PropConstOverOuterJoin(p.ctx, joinConds, predicates, outerTable.Schema(), innerTable.Schema(), nullSensitive)
p.AttachOnConds(joinConds)
return predicates
}
// GetPartitionByCols extracts 'partition by' columns from the Window.
func (p *LogicalWindow) GetPartitionByCols() []*expression.Column {
partitionCols := make([]*expression.Column, 0, len(p.PartitionBy))
for _, partitionItem := range p.PartitionBy {
partitionCols = append(partitionCols, partitionItem.Col)
}
return partitionCols
}
// PredicatePushDown implements LogicalPlan PredicatePushDown interface.
func (p *LogicalWindow) PredicatePushDown(predicates []expression.Expression) ([]expression.Expression, LogicalPlan) {
canBePushed := make([]expression.Expression, 0, len(predicates))
canNotBePushed := make([]expression.Expression, 0, len(predicates))
partitionCols := expression.NewSchema(p.GetPartitionByCols()...)
for _, cond := range predicates {
// We can push predicate beneath Window, only if all of the
// extractedCols are part of partitionBy columns.
if expression.ExprFromSchema(cond, partitionCols) {
canBePushed = append(canBePushed, cond)
} else {
canNotBePushed = append(canNotBePushed, cond)
}
}
p.baseLogicalPlan.PredicatePushDown(canBePushed)
return canNotBePushed, p
}
// PredicatePushDown implements LogicalPlan PredicatePushDown interface.
func (p *LogicalMemTable) PredicatePushDown(predicates []expression.Expression) ([]expression.Expression, LogicalPlan) {
if p.Extractor != nil {
predicates = p.Extractor.Extract(p.ctx, p.schema, p.names, predicates)
}
return predicates, p.self
}
func (*ppdSolver) name() string {
return "predicate_push_down"
}