public interface Converter extends RelNode
Converterto indicate that it converts a physical attribute, or
trait, of a relational expression from one value to another.
Sometimes this conversion is expensive; for example, to convert a non-distinct to a distinct object stream, we have to clone every object in the input.
A converter does not change the logical expression being evaluated; after
conversion, the number of rows and the values of those rows will still be the
same. By declaring itself to be a converter, a relational expression is
telling the planner about this equivalence, and the planner groups
expressions which are logically equivalent but have different physical traits
into groups called
In principle one could devise converters which change multiple traits
simultaneously (say change the sort-order and the physical location of a
relational expression). In which case, the method
would return a
RelTraitSet. But for
simplicity, this class only allows one trait to be converted at a
time; all other traits are assumed to be preserved.
|Modifier and Type||Method and Description|
Returns the sole input relational expression
Returns the trait of the input relational expression.
Returns the definition of trait which this converter works on.
accept, accept, childrenAccept, collectVariablesSet, collectVariablesUsed, computeSelfCost, computeSelfCost, copy, estimateRowCount, explain, getChildExps, getCollationList, getConvention, getCorrelVariable, getExpectedInputRowType, getInput, getInputs, getQuery, getRelTypeName, getRows, getRowType, getTable, getVariablesSet, getVariablesStopped, isDistinct, isKey, isValid, isValid, metadata, onRegister, recomputeDigest, register, replaceInput
The input relational expression (matched by the rule) must possess
this trait and have the value given by
getInputTraits(), and the
traits of the output of this converter given by
have one trait altered and the other orthogonal traits will be the same.
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