/**
* This overload variant of optimizeStatement is used by subclass CursorNode (as well as a minion
* for the no-arg variant).
*
* @param offset Any OFFSET row count, or null
* @param fetchFirst Any FETCH FIRST row count or null
* @exception StandardException Thrown on error
* @see DMLStatementNode#optimizeStatement()
*/
protected void optimizeStatement(ValueNode offset, ValueNode fetchFirst)
throws StandardException {
resultSet = resultSet.preprocess(getCompilerContext().getNumTables(), null, (FromList) null);
resultSet = resultSet.optimize(getDataDictionary(), null, 1.0d);
resultSet = resultSet.modifyAccessPaths();
// Any OFFSET/FETCH FIRST narrowing must be done *after* any rewrite of
// the query tree (if not, underlying GROUP BY fails), but *before* the
// final scroll insensitive result node set is added - that one needs
// to sit on top - so now is the time.
//
// This example statement fails if we wrap *before* the optimization
// above:
// select max(a) from t1 group by b fetch first row only
//
// A java.sql.ResultSet#previous on a scrollable result set will fail
// if we don't wrap *after* the ScrollInsensitiveResultSetNode below.
//
// We need only wrap the RowCountNode set if at least one of the
// clauses is present.
if (offset != null || fetchFirst != null) {
resultSet = wrapRowCountNode(resultSet, offset, fetchFirst);
}
/* If this is a cursor, then we
* need to generate a new ResultSetNode to enable the scrolling
* on top of the tree before modifying the access paths.
*/
if (this instanceof CursorNode) {
ResultColumnList siRCList;
ResultColumnList childRCList;
ResultSetNode siChild = resultSet;
/* We get a shallow copy of the ResultColumnList and its
* ResultColumns. (Copy maintains ResultColumn.expression for now.)
*/
siRCList = resultSet.getResultColumns();
childRCList = siRCList.copyListAndObjects();
resultSet.setResultColumns(childRCList);
/* Replace ResultColumn.expression with new VirtualColumnNodes
* in the ScrollInsensitiveResultSetNode's ResultColumnList. (VirtualColumnNodes include
* pointers to source ResultSetNode, this, and source ResultColumn.)
*/
siRCList.genVirtualColumnNodes(resultSet, childRCList);
/* Finally, we create the new ScrollInsensitiveResultSetNode */
resultSet =
(ResultSetNode)
getNodeFactory()
.getNode(
C_NodeTypes.SCROLL_INSENSITIVE_RESULT_SET_NODE,
resultSet,
siRCList,
null,
getContextManager());
// Propagate the referenced table map if it's already been created
if (siChild.getReferencedTableMap() != null) {
resultSet.setReferencedTableMap((JBitSet) siChild.getReferencedTableMap().clone());
}
}
}
/**
* Preprocess a ResultSetNode - this currently means: o Generating a referenced table map for each
* ResultSetNode. o Putting the WHERE and HAVING clauses in conjunctive normal form (CNF). o
* Converting the WHERE and HAVING clauses into PredicateLists and classifying them. o Ensuring
* that a ProjectRestrictNode is generated on top of every FromBaseTable and generated in place of
* every FromSubquery. o Pushing single table predicates down to the new ProjectRestrictNodes.
*
* @param numTables The number of tables in the DML Statement
* @param gbl The group by list, if any
* @param fromList The from list, if any
* @return ResultSetNode at top of preprocessed tree.
* @exception StandardException Thrown on error
*/
public ResultSetNode preprocess(int numTables, GroupByList gbl, FromList fromList)
throws StandardException {
// Push the order by list down to the ResultSet
if (orderByList != null) {
// If we have more than 1 ORDERBY columns, we may be able to
// remove duplicate columns, e.g., "ORDER BY 1, 1, 2".
if (orderByList.size() > 1) {
orderByList.removeDupColumns();
}
subquery.pushOrderByList(orderByList);
orderByList = null;
}
subquery.pushOffsetFetchFirst(offset, fetchFirst, hasJDBClimitClause);
/* We want to chop out the FromSubquery from the tree and replace it
* with a ProjectRestrictNode. One complication is that there may be
* ColumnReferences above us which point to the FromSubquery's RCL.
* What we want to return is a tree with a PRN with the
* FromSubquery's RCL on top. (In addition, we don't want to be
* introducing any redundant ProjectRestrictNodes.)
* Another complication is that we want to be able to only push
* projections and restrictions down to this ProjectRestrict, but
* we want to be able to push them through as well.
* So, we:
* o call subquery.preprocess() which returns a tree with
* a SelectNode or a RowResultSetNode on top.
* o If the FSqry is flattenable(), then we return (so that the
* caller can then call flatten()), otherwise we:
* o generate a PRN, whose RCL is the FSqry's RCL, on top of the result.
* o create a referencedTableMap for the PRN which represents
* the FSqry's tableNumber, since ColumnReferences in the outer
* query block would be referring to that one.
* (This will allow us to push restrictions down to the PRN.)
*/
subquery = subquery.preprocess(numTables, gbl, fromList);
/* Return if the FSqry is flattenable()
* NOTE: We can't flatten a FromSubquery if there is a group by list
* because the group by list must be ColumnReferences. For:
* select c1 from v1 group by c1,
* where v1 is select 1 from t1
* The expression under the last redundant ResultColumn is an IntConstantNode,
* not a ColumnReference.
* We also do not flatten a subquery if tableProperties is non-null,
* as the user is specifying 1 or more properties for the derived table,
* which could potentially be lost on the flattening.
* RESOLVE - this is too restrictive.
*/
if ((gbl == null || gbl.size() == 0)
&& tableProperties == null
&& subquery.flattenableInFromSubquery(fromList)) {
/* Set our table map to the subquery's table map. */
setReferencedTableMap(subquery.getReferencedTableMap());
return this;
}
return extractSubquery(numTables);
}