net.sf.saffron.rel
Class TableAccessRel

java.lang.Object
  |
  +--net.sf.saffron.rel.SaffronRel
        |
        +--net.sf.saffron.rel.TableAccessRel

Direct Known Subclasses:

JavaTableAccessRel

public class TableAccessRel

extends SaffronRel

A TableAccessRel reads all the rows from a SaffronTable.

If the table is a JdbcTable, then this is literally possible. But for other kinds of tables, there may be many ways to read the data from the table. For some kinds of table, it may not even be possible to read all of the rows unless some narrowing constraint is applied. In the example of the ReflectSchema schema,

select from fields

cannot be implemented, but

select from fields as f
 where f.getClass().getName().equals("java.lang.String")

can. It is the optimizer's responsibility to find these ways, by applying transformation rules.

Since:

10 November, 2001

Version:

$Id: //open/saffron/src/net/sf/saffron/rel/TableAccessRel.java#5 $

Author:

jhyde

Field Summary

protected SaffronConnection	connection The connection to Saffron.
protected SaffronTable	table The table definition.

Fields inherited from class net.sf.saffron.rel.SaffronRel

cluster, digest, emptyArray, id, nextId, rowType

Constructor Summary

TableAccessRel(VolcanoCluster cluster, SaffronTable table, SaffronConnection connection)

Method Summary

Object	clone()
PlanCost	computeSelfCost(SaffronPlanner planner) Returns the cost of this plan (not including children).
SaffronType	deriveRowType()
void	explain(PlanWriter pw)
SaffronConnection	getConnection()
double	getRows() Returns an estimate of the number of rows this relational expression will return.
SaffronTable	getTable() If this relational expression represents an access to a table, returns that table, otherwise returns null.

Methods inherited from class net.sf.saffron.rel.SaffronRel

childrenAccept, computeDigest, getChildExps, getCluster, getConvention, getCorrelVariable, getId, getInput, getInputs, getOrCreateCorrelVariable, getQualifier, getQuery, getRelTypeName, getRowType, getVariablesStopped, implement, implementFieldAccess, isAccessTo, isDistinct, onRegister, recomputeDigest, register, registerCorrelVariable, replaceInput, setCorrelVariable, toString

Methods inherited from class java.lang.Object

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

Field Detail

connection

protected SaffronConnection connection

The connection to Saffron.

table

protected SaffronTable table

The table definition.

Constructor Detail

TableAccessRel

public TableAccessRel(VolcanoCluster cluster,
                      SaffronTable table,
                      SaffronConnection connection)

Method Detail

getConnection

public SaffronConnection getConnection()

getRows

public double getRows()

Description copied from class: SaffronRel

Returns an estimate of the number of rows this relational expression will return.

Overrides:

getRows in class SaffronRel

getTable

public SaffronTable getTable()

Description copied from class: SaffronRel

If this relational expression represents an access to a table, returns that table, otherwise returns null.

Overrides:

getTable in class SaffronRel

clone

public Object clone()

Specified by:

clone in class SaffronRel

computeSelfCost

public PlanCost computeSelfCost(SaffronPlanner planner)

Description copied from class: SaffronRel

Returns the cost of this plan (not including children). The base implementation throws an error; derived classes should override.

Overrides:

computeSelfCost in class SaffronRel

deriveRowType

public SaffronType deriveRowType()

Specified by:

deriveRowType in class SaffronRel

explain

public void explain(PlanWriter pw)

Overrides:

explain in class SaffronRel