org.apache.derby.impl.sql.compile

Class CursorNode

java.lang.Object

org.apache.derby.impl.sql.compile.QueryTreeNode

org.apache.derby.impl.sql.compile.StatementNode

org.apache.derby.impl.sql.compile.CursorNode

All Implemented Interfaces:

Visitable

public class CursorNode
extends StatementNode

A CursorNode represents a result set that can be returned to a client. A cursor can be a named cursor created by the DECLARE CURSOR statement, or it can be an unnamed cursor associated with a SELECT statement (more precisely, a table expression that returns rows to the client). In the latter case, the cursor does not have a name.

Field Summary

Fields

Modifier and Type	Field and Description
static int	READ_ONLY

Method Summary

Modifier and Type	Method and Description
void	bindStatement() Bind this CursorNode.
java.lang.Object	getCursorInfo() Get information about this cursor.
boolean	isAtomic() A read statement is atomic (DMLMod overrides us) if there are no work units, and no SELECT nodes, or if its SELECT nodes are all arguments to a function.
ResultDescription	makeResultDescription() Make a ResultDescription for use in a PreparedStatement.
boolean	needsSavepoint() Returns whether or not this Statement requires a set/clear savepoint around its execution.
void	optimizeStatement() Optimize a DML statement (which is the only type of statement that should need optimizing, I think).
boolean	referencesSessionSchema() Return true if the node references SESSION schema tables (temporary or permanent)
java.lang.String	toString() Convert this object to a String.
TableDescriptor[]	updateIndexStatisticsFor() Returns a list of base tables for which the index statistics of the associated indexes should be updated.

Methods inherited from class org.apache.derby.impl.sql.compile.StatementNode

executeSchemaName, executeStatementName, generate, getSPSName

Methods inherited from class org.apache.derby.impl.sql.compile.QueryTreeNode

accept, addTag, bindOffsetFetch, bindRowMultiSet, bindUserCatalogType, bindUserType, checkReliability, checkReliability, createTypeDependency, getBeginOffset, getDataDictionary, getEndOffset, getExecutionFactory, getGenericConstantActionFactory, getOffsetOrderedNodes, getOptimizerFactory, getOptimizerTracer, getParameterTypes, getUDTDesc, makeConstantAction, makeTableName, makeTableName, optimizerTracingIsOn, orReliability, setBeginOffset, setEndOffset, taggedWith, treePrint

Methods inherited from class java.lang.Object

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

Field Detail

READ_ONLY

public static final int READ_ONLY

See Also:

Constant Field Values

Method Detail

toString

public java.lang.String toString()

Convert this object to a String. See comments in QueryTreeNode.java for how this should be done for tree printing.

Overrides:

toString in class StatementNode

Returns:

This object as a String

bindStatement

public void bindStatement()
                   throws StandardException

Bind this CursorNode. This means looking up tables and columns and getting their types, and figuring out the result types of all expressions, as well as doing view resolution, permissions checking, etc. It also includes determining whether an UNSPECIFIED cursor is updatable or not, and verifying that an UPDATE cursor actually is.

Overrides:

bindStatement in class StatementNode

Throws:

StandardException - Thrown on error

referencesSessionSchema

public boolean referencesSessionSchema()
                                throws StandardException

Return true if the node references SESSION schema tables (temporary or permanent)

Overrides:

referencesSessionSchema in class QueryTreeNode

Returns:

true if references SESSION schema tables, else false

Throws:

StandardException - Thrown on error

optimizeStatement

public void optimizeStatement()
                       throws StandardException

Optimize a DML statement (which is the only type of statement that should need optimizing, I think). This method over-rides the one in QueryTreeNode. This method takes a bound tree, and returns an optimized tree. It annotates the bound tree rather than creating an entirely new tree. Throws an exception if the tree is not bound, or if the binding is out of date.

Throws:

StandardException - Thrown on error

needsSavepoint

public boolean needsSavepoint()

Returns whether or not this Statement requires a set/clear savepoint around its execution. The following statement "types" do not require them: Cursor - unnecessary and won't work in a read only environment Xact - savepoint will get blown away underneath us during commit/rollback

Overrides:

needsSavepoint in class StatementNode

Returns:

boolean Whether or not this Statement requires a set/clear savepoint

getCursorInfo

public java.lang.Object getCursorInfo()
                               throws StandardException

Get information about this cursor. For sps, this is info saved off of the original query tree (the one for the underlying query).

Overrides:

getCursorInfo in class StatementNode

Returns:

the cursor info

Throws:

StandardException - thrown if generation fails

updateIndexStatisticsFor

public TableDescriptor[] updateIndexStatisticsFor()
                                           throws StandardException

Returns a list of base tables for which the index statistics of the associated indexes should be updated.

Overrides:

updateIndexStatisticsFor in class StatementNode

Returns:

A list of table descriptors (potentially empty).

Throws:

StandardException - if accessing the index descriptors of a base table fails

makeResultDescription

public ResultDescription makeResultDescription()

Make a ResultDescription for use in a PreparedStatement. ResultDescriptions are visible to JDBC only for cursor statements. For other types of statements, they are only used internally to get descriptions of the base tables being affected. For example, for an INSERT statement, the ResultDescription describes the rows in the table being inserted into, which is useful when the values being inserted are of a different type or length than the columns in the base table.

Overrides:

makeResultDescription in class StatementNode

Returns:

A ResultDescription for this DML statement

isAtomic

public boolean isAtomic()
                 throws StandardException

A read statement is atomic (DMLMod overrides us) if there are no work units, and no SELECT nodes, or if its SELECT nodes are all arguments to a function. This is admittedly a bit simplistic, what if someone has:

        VALUES myfunc(SELECT max(c.commitFunc()) FROM T) 
 

but we aren't going too far out of our way to catch every possible wierd case. We basically want to be permissive w/o allowing someone to partially commit a write.

Overrides:

isAtomic in class StatementNode

Returns:

true if the statement is atomic

Throws:

StandardException - on error