func CanIUseThisIndexForThisWhereClause(index catalog.RangeIndex, where ast.Expression, bucket string) (bool, plan.ScanRanges, ast.Expression, error) {
// convert the index key to formal notation
indexKeyFormal, err := IndexKeyInFormalNotation(index.Key(), bucket)
if err != nil {
return false, nil, nil, err
}
// put the where clause into conjunctive normal form
ennf := ast.NewExpressionNNF()
whereNNF, err := where.Accept(ennf)
if err != nil {
return false, nil, nil, err
}
ecnf := ast.NewExpressionCNF()
whereCNF, err := whereNNF.Accept(ecnf)
if err != nil {
return false, nil, nil, err
}
switch whereCNF := whereCNF.(type) {
case *ast.AndOperator:
// this is an and, we can try to satisfy individual operands
found := false
rranges := plan.ScanRanges{}
for _, oper := range whereCNF.Operands {
// see if the where clause expression is sargable with respect to the index key
es := NewExpressionSargable(indexKeyFormal[0])
oper.Accept(es)
if es.IsSargable() {
found = true
for _, ran := range es.ScanRanges() {
rranges = MergeRanges(rranges, ran)
clog.To(planner.CHANNEL, "now ranges are: %v", rranges)
}
}
}
if found {
return true, rranges, nil, nil
}
default:
// not an and, we must satisfy the whole expression
// see if the where clause expression is sargable with respect to the index key
es := NewExpressionSargable(indexKeyFormal[0])
whereCNF.Accept(es)
if es.IsSargable() {
return true, es.ScanRanges(), nil, nil
}
}
// cannot use this index
return false, nil, nil, nil
}
func CanIUseThisIndexForThisProjectionNoWhereNoGroupClause(index catalog.RangeIndex, resultExprList ast.ResultExpressionList, bucket string) (bool, plan.ScanRanges, ast.Expression, error) {
// convert the index key to formal notation
indexKeyFormal, err := IndexKeyInFormalNotation(index.Key(), bucket)
if err != nil {
return false, nil, nil, err
}
// FIXME only looking at first element in key right now
deps := ast.ExpressionList{indexKeyFormal[0]}
clog.To(planner.CHANNEL, "index deps are: %v", deps)
depChecker := ast.NewExpressionFunctionalDependencyCheckerFull(deps)
// start looking at the projection
allAggregateFunctionsMin := true
for _, resultExpr := range resultExprList {
// presence of * means we cannot use index on field, must see all (for this particular optimization)
if resultExpr.Star {
return false, nil, nil, nil
}
switch expr := resultExpr.Expr.(type) {
case ast.AggregateFunctionCallExpression:
_, isMin := expr.(*ast.FunctionCallMin)
if !isMin {
clog.To(planner.CHANNEL, "projection not MIN")
allAggregateFunctionsMin = false
}
// aggregates all take 1 operand
operands := expr.GetOperands()
if len(operands) < 1 {
return false, nil, nil, nil
}
aggOperand := operands[0]
// preence of * means we cannot use this index, must see all (for this particular optimization)
if aggOperand.Star {
return false, nil, nil, nil
}
// look at dependencies inside this operand
_, err := depChecker.Visit(aggOperand.Expr)
if err != nil {
return false, nil, nil, nil
}
default:
// all expressions must be aggregates for this particular optimization
return false, nil, nil, nil
}
}
// if we made it this far, we can in fact use the index
// doing a scan of all non-eliminatable items (non-NULL, non-MISSING)
dummyOp := ast.NewIsNotNullOperator(indexKeyFormal[0])
es := NewExpressionSargable(indexKeyFormal[0])
dummyOp.Accept(es)
if es.IsSargable() {
ranges := es.ScanRanges()
if allAggregateFunctionsMin {
for _, r := range ranges {
r.Limit = 1
}
}
return true, ranges, nil, nil
}
clog.Error(fmt.Errorf("expected this to never happen"))
// cannot use this index
return false, nil, nil, nil
}
func DoesIndexCoverStatement(index catalog.RangeIndex, stmt *ast.SelectStatement) bool {
if stmt.From.Over != nil {
// index cannot cover queries containing OVER right now
return false
}
// convert the index key to formal notation
indexKeyFormal, err := IndexKeyInFormalNotation(index.Key(), stmt.From.As)
if err != nil {
return false
}
deps := ast.ExpressionList{}
for _, indexKey := range indexKeyFormal {
deps = append(deps, indexKey)
}
clog.To(planner.CHANNEL, "index deps are: %v", deps)
depChecker := ast.NewExpressionFunctionalDependencyCheckerFull(deps)
// first check the projection
for _, resultExpr := range stmt.Select {
if resultExpr.Star == true || resultExpr.Expr == nil {
// currently cannot cover *
return false
}
_, err := depChecker.Visit(resultExpr.Expr)
if err != nil {
return false
}
}
if stmt.Where != nil {
_, err = depChecker.Visit(stmt.Where)
if err != nil {
return false
}
}
if stmt.GroupBy != nil {
for _, groupExpr := range stmt.GroupBy {
_, err = depChecker.Visit(groupExpr)
if err != nil {
return false
}
}
if stmt.Having != nil {
_, err = depChecker.Visit(stmt.Having)
if err != nil {
return false
}
}
}
if stmt.OrderBy != nil {
for _, orderExpr := range stmt.OrderBy {
_, err = depChecker.Visit(orderExpr.Expr)
if err != nil {
return false
}
}
}
// if we go this far it is covered
return true
}
