Package io.prestosql.sql.planner.optimizations

Class UnaliasSymbolReferences

java.lang.Object

io.prestosql.sql.planner.optimizations.UnaliasSymbolReferences

All Implemented Interfaces:

PlanOptimizer

public class UnaliasSymbolReferences
extends Object
implements PlanOptimizer

Re-maps symbol references that are just aliases of each other (e.g., due to projections like $0 := $1)

E.g.,

Output[$0, $1] -> Project[$0 := $2, $1 := $3 * 100] -> Aggregate[$2, $3 := sum($4)] -> ...

gets rewritten as

Output[$2, $1] -> Project[$2, $1 := $3 * 100] -> Aggregate[$2, $3 := sum($4)] -> ...

Constructor Summary

Constructors

Constructor	Description
UnaliasSymbolReferences(Metadata metadata)

Method Summary

Modifier and Type	Method	Description
PlanNode	optimize(PlanNode plan, Session session, TypeProvider types, SymbolAllocator symbolAllocator, PlanNodeIdAllocator idAllocator, WarningCollector warningCollector)
NodeAndMappings	reallocateSymbols(PlanNode plan, List<Symbol> fields, SymbolAllocator symbolAllocator)	Replace all symbols in the plan with new symbols.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

UnaliasSymbolReferences

public UnaliasSymbolReferences(Metadata metadata)

Method Detail

optimize

public PlanNode optimize(PlanNode plan,
                         Session session,
                         TypeProvider types,
                         SymbolAllocator symbolAllocator,
                         PlanNodeIdAllocator idAllocator,
                         WarningCollector warningCollector)

Specified by:

optimize in interface PlanOptimizer

reallocateSymbols

public NodeAndMappings reallocateSymbols(PlanNode plan,
                                         List<Symbol> fields,
                                         SymbolAllocator symbolAllocator)

Replace all symbols in the plan with new symbols. The returned plan has different output than the original plan. Also, the order of symbols might change during symbol replacement. Symbols in the list `fields` are replaced maintaining the order so they might be used to match original symbols with their replacements. Replacing symbols helps avoid collisions when symbols or parts of the plan are reused.