Interface RequiredRowOrdering
- All Known Implementing Classes:
OrderByList
public interface RequiredRowOrdering
This interface provides a representation of the required ordering of rows
from a ResultSet. Different operations can require ordering: ORDER BY,
DISTINCT, GROUP BY. Some operations, like ORDER BY, require that the
columns be ordered a particular way, while others, like DISTINCT and
GROUP BY, reuire only that there be no duplicates in the result.
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Field Summary
FieldsModifier and TypeFieldDescriptionstatic final int
static final int
static final int
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Method Summary
Modifier and TypeMethodDescriptionvoid
estimateCost
(double estimatedInputRows, RowOrdering rowOrdering, CostEstimate resultCost) Estimate the cost of doing a sort for this row ordering, given the number of rows to be sorted.boolean
void
Indicate that a sort is necessary to fulfill this required ordering.void
Indicate that a sort is *NOT* necessary to fulfill this required ordering.int
sortRequired
(RowOrdering rowOrdering, OptimizableList optimizableList, int[] proposedJoinOrder) Tell whether sorting is required for this RequiredRowOrdering, given a RowOrdering.int
sortRequired
(RowOrdering rowOrdering, JBitSet tableMap, OptimizableList optimizableList, int[] proposedJoinOrder) Tell whether sorting is required for this RequiredRowOrdering, given a RowOrdering representing a partial join order, and a bit map telling what tables are represented in the join order.
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Field Details
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SORT_REQUIRED
static final int SORT_REQUIRED- See Also:
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ELIMINATE_DUPS
static final int ELIMINATE_DUPS- See Also:
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NOTHING_REQUIRED
static final int NOTHING_REQUIRED- See Also:
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Method Details
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sortRequired
int sortRequired(RowOrdering rowOrdering, OptimizableList optimizableList, int[] proposedJoinOrder) throws StandardException Tell whether sorting is required for this RequiredRowOrdering, given a RowOrdering.- Parameters:
rowOrdering
- The order of rows in questionoptimizableList
- The list of join participantsproposedJoinOrder
- The current join order being considered by the optimizer. We need to look into this to determine if the outer optimizables are single row result set if the order by column is on an inner optimizable and that inner optimizable is not a one.proposedJoinOrder
is a map ontooptimizableList
: it contains indexes of optimizables in that list in the join order proposed, cf.OptimizerImpl#proposedJoinOrder
.- Returns:
- SORT_REQUIRED if sorting is required, ELIMINATE_DUPS if no sorting is required but duplicates must be eliminated (i.e. the rows are in the right order but there may be duplicates), NOTHING_REQUIRED is no operation is required
- Throws:
StandardException
- Thrown on error
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sortRequired
int sortRequired(RowOrdering rowOrdering, JBitSet tableMap, OptimizableList optimizableList, int[] proposedJoinOrder) throws StandardException Tell whether sorting is required for this RequiredRowOrdering, given a RowOrdering representing a partial join order, and a bit map telling what tables are represented in the join order. This is useful for reducing the number of cases the optimizer has to consider.- Parameters:
rowOrdering
- The order of rows in the partial join ordertableMap
- A bit map of the tables in the partial join orderoptimizableList
- The list of join participantsproposedJoinOrder
- The current join order being considered by the optimizer. We need to look into this to determine if the outer optimizables are single row result set if the order by column is on an inner optimizable and that inner optimizable is not a one.proposedJoinOrder
is a map ontooptimizableList
: it contains indexes of optimizables in that list in the join order proposed, cf.OptimizerImpl#proposedJoinOrder
. DERBY-3926 and DERBY-6148- Returns:
- SORT_REQUIRED if sorting is required, ELIMINATE_DUPS if no sorting is required by duplicates must be eliminated (i.e. the rows are in the right order but there may be duplicates), NOTHING_REQUIRED is no operation is required
- Throws:
StandardException
- Thrown on error
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estimateCost
void estimateCost(double estimatedInputRows, RowOrdering rowOrdering, CostEstimate resultCost) throws StandardException Estimate the cost of doing a sort for this row ordering, given the number of rows to be sorted. This does not take into account whether the sort is really needed. It also estimates the number of result rows.- Parameters:
estimatedInputRows
- The estimated number of rows to sortrowOrdering
- The ordering of the input rowsresultCost
- A place to store the resulting cost- Throws:
StandardException
- Thrown on error
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sortNeeded
void sortNeeded()Indicate that a sort is necessary to fulfill this required ordering. This method may be called many times during a single optimization. -
sortNotNeeded
void sortNotNeeded()Indicate that a sort is *NOT* necessary to fulfill this required ordering. This method may be called many times during a single optimization. -
getSortNeeded
boolean getSortNeeded()
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