private static AlgebraNode InstantiateCte(AlgebraNode algebrizedCte, CommonTableBinding commonTableBinding, TableRefBinding commonTableRefBinding)
{
// Replace row buffers to base tables by new ones. This must be done because a CTE could be referenced multiple times.
// Since same row buffer entries means that the underlying data will be stored in the same physical data slot this
// will lead to problems if, for example, two instances of the same CTE are joined together. Any join condition that
// operates on the same column will always compare data coming from the same join side (and therefor will always
// evaluate to true).
//
// Some notes on the implementation:
//
// 1. Note that just replacing references to row buffers of base tables in RowBufferExpression is not enough;
// instead they must also be replaced in output lists, defined value references (esp. ConcatAlgebraNode) etc.
// 2. Also note that although the QueryNodes are re-algebrized every time a CTE is references the expressions
// are still copied from the QueryNodes (instead of cloned). Therefore two algrebrized CTEs will share the same
// expression AST instances. That means that replacing the row buffers leads to failure.
// HACK: This is a workaround for issue 2. However,
// I am not quite sure how one should implement row buffer entry replacement without cloning the algebrized query.
algebrizedCte = (AlgebraNode)algebrizedCte.Clone();
CteTableDefinedValuesReinitializer cteTableDefinedValuesReinitializer = new CteTableDefinedValuesReinitializer();
cteTableDefinedValuesReinitializer.Visit(algebrizedCte);
RowBufferEntry[] outputList = algebrizedCte.OutputList;
int skipRecursionLevel = commonTableBinding.IsRecursive ? 1 : 0;
// Rename the query columns to the CTE columns
List <ComputedValueDefinition> definedValues = new List <ComputedValueDefinition>();
for (int i = 0; i < commonTableRefBinding.ColumnRefs.Length; i++)
{
RowBufferEntry targetRowBufferEntry = commonTableRefBinding.ColumnRefs[i].ValueDefinition.Target;
RowBufferEntry sourceRowBufferEntry = outputList[i + skipRecursionLevel];
ComputedValueDefinition definedValue = new ComputedValueDefinition();
definedValue.Target = targetRowBufferEntry;
definedValue.Expression = new RowBufferEntryExpression(sourceRowBufferEntry);
definedValues.Add(definedValue);
}
ComputeScalarAlgebraNode computeScalarAlgebraNode = new ComputeScalarAlgebraNode();
computeScalarAlgebraNode.Input = algebrizedCte;
computeScalarAlgebraNode.DefinedValues = definedValues.ToArray();
return(computeScalarAlgebraNode);
}
private static AlgebraNode InstantiateCte(AlgebraNode algebrizedCte, CommonTableBinding commonTableBinding, TableRefBinding commonTableRefBinding)
{
// Replace row buffers to base tables by new ones. This must be done because a CTE could be referenced multiple times.
// Since same row buffer entries means that the underlying data will be stored in the same physical data slot this
// will lead to problems if, for example, two instances of the same CTE are joined together. Any join condition that
// operates on the same column will always compare data coming from the same join side (and therefor will always
// evaluate to true).
//
// Some notes on the implementation:
//
// 1. Note that just replacing references to row buffers of base tables in RowBufferExpression is not enough;
// instead they must also be replaced in output lists, defined value references (esp. ConcatAlgebraNode) etc.
// 2. Also note that although the QueryNodes are re-algebrized every time a CTE is references the expressions
// are still copied from the QueryNodes (instead of cloned). Therefore two algrebrized CTEs will share the same
// expression AST instances. That means that replacing the row buffers leads to failure.
// HACK: This is a workaround for issue 2. However,
// I am not quite sure how one should implement row buffer entry replacement without cloning the algebrized query.
algebrizedCte = (AlgebraNode) algebrizedCte.Clone();
CteTableDefinedValuesReinitializer cteTableDefinedValuesReinitializer = new CteTableDefinedValuesReinitializer();
cteTableDefinedValuesReinitializer.Visit(algebrizedCte);
RowBufferEntry[] outputList = algebrizedCte.OutputList;
int skipRecursionLevel = commonTableBinding.IsRecursive ? 1 : 0;
// Rename the query columns to the CTE columns
List<ComputedValueDefinition> definedValues = new List<ComputedValueDefinition>();
for (int i = 0; i < commonTableRefBinding.ColumnRefs.Length; i++)
{
RowBufferEntry targetRowBufferEntry = commonTableRefBinding.ColumnRefs[i].ValueDefinition.Target;
RowBufferEntry sourceRowBufferEntry = outputList[i + skipRecursionLevel];
ComputedValueDefinition definedValue = new ComputedValueDefinition();
definedValue.Target = targetRowBufferEntry;
definedValue.Expression = new RowBufferEntryExpression(sourceRowBufferEntry);
definedValues.Add(definedValue);
}
ComputeScalarAlgebraNode computeScalarAlgebraNode = new ComputeScalarAlgebraNode();
computeScalarAlgebraNode.Input = algebrizedCte;
computeScalarAlgebraNode.DefinedValues = definedValues.ToArray();
return computeScalarAlgebraNode;
}
