com.akiban.sql.parser
Class SubqueryNode

java.lang.Object
  com.akiban.sql.parser.QueryTreeNode
      com.akiban.sql.parser.ValueNode
          com.akiban.sql.parser.SubqueryNode

All Implemented Interfaces:

Visitable

public class SubqueryNode
extends ValueNode

A SubqueryNode represents a subquery. Subqueries return values to their outer queries. An quantified subquery is one that appears under a quantified operator (like IN or EXISTS) - quantified subqueries can return more than one value per invocation. An expression subquery is one that is not directly under a quantified operator - expression subqueries are allowed to return at most one value per invocation (returning no value is considered to be equivalent to returning NULL). There are a large number of subquery types. Because of the large number of types, and the large amount of shared code, we have decided to have 1 SubqueryNode without any subclasses. The subquery type (and operator) is encoded in the subqueryType field. The query optimizer is responsible for optimizing subqueries, and also for transforming them so that code can be generated for them. The optimizer may eliminate some subqueries by transforming them into joins, or it may change the internal form of a subquery (for example, transforming 'where x in (select y from z where ...)' into 'where (select true from z where x = y and ...)'). Note that aggregates present some additional issues. A transformation such as:

where x in (SELECT expression FROM z)

has to be treated specially if expression has an aggregate. We change it to:

where x = (SELECT true FROM (SELECT MAX(x) FROM z) WHERE SQLCOL1 = y)

Nested Class Summary

static class

SubqueryNode.SubqueryType

Field Summary

Fields inherited from class com.akiban.sql.parser.QueryTreeNode

AUTOINCREMENT_CREATE_MODIFY, AUTOINCREMENT_INC_INDEX, AUTOINCREMENT_IS_AUTOINCREMENT_INDEX, AUTOINCREMENT_START_INDEX

Constructor Summary

SubqueryNode()

Method Summary

void	copyFrom(QueryTreeNode node) Fill this node with a deep copy of the given node.
ValueNode	getFetchFirst() Get FETCH FIRST (used to construct FROM only), cf.
ValueNode	getLeftOperand()
ValueNode	getOffset() Get OFFSET (used to construct FROM only), cf.
OrderByList	getOrderByList() Get ORDER BY list (used to construct FROM only), cf.
ResultSetNode	getResultSet() Return the resultSet for this SubqueryNode.
SubqueryNode.SubqueryType	getSubqueryType() Return the type of this subquery.
void	init(Object resultSet, Object subqueryType, Object leftOperand, Object orderCols, Object offset, Object fetchFirst) Initializer.
protected boolean	isEquivalent(ValueNode o) Tests if this node is equivalent to the specified ValueNode.
void	printSubNodes(int depth) Prints the sub-nodes of this object.
void	setResultSet(ResultSetNode resultSet)
void	setSubqueryType(SubqueryNode.SubqueryType subqueryType) Set the type of this subquery.
String	toString() Convert this object to a String.

Methods inherited from class com.akiban.sql.parser.ValueNode

getColumnName, getSchemaName, getSourceResultColumn, getTableName, getType, getTypeId, init, isBinaryEqualsOperatorNode, isBooleanFalse, isBooleanTrue, isConstantExpression, isInListProbeNode, isParameterNode, isRelationalOperator, isSameNodeType, setNullability, setType

Methods inherited from class com.akiban.sql.parser.QueryTreeNode

accept, convertDefaultNode, debugFlush, debugPrint, formatNodeString, getBeginOffset, getDebugOutput, getEndOffset, getNodeFactory, getNodeType, getNullNode, getParserContext, getStatementType, getUserData, init, init, init, init, init, init, init, init, init, init, init, init, isInstanceOf, makeTableName, makeTableName, nodeHeader, printLabel, setBeginOffset, setDebugOutput, setEndOffset, setNodeType, setParserContext, setUserData, stackPrint, treePrint, treePrint, treePrint

Methods inherited from class java.lang.Object

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

Constructor Detail

SubqueryNode

public SubqueryNode()

Method Detail

init

public void init(Object resultSet,
                 Object subqueryType,
                 Object leftOperand,
                 Object orderCols,
                 Object offset,
                 Object fetchFirst)

Initializer.

Overrides:

init in class QueryTreeNode

Parameters:

resultSet - The ResultSetNode for the subquery

subqueryType - The type of the subquery

leftOperand - The left operand, if any, of the subquery

orderCols - ORDER BY list

offset - OFFSET n ROWS

fetchFirst - FETCH FIRST n ROWS ONLY

copyFrom

public void copyFrom(QueryTreeNode node)
              throws StandardException

Fill this node with a deep copy of the given node.

Overrides:

copyFrom in class ValueNode

Throws:

StandardException

toString

public 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 ValueNode

Returns:

This object as a String

printSubNodes

public void printSubNodes(int depth)

Prints the sub-nodes of this object. See QueryTreeNode.java for how tree printing is supposed to work.

Overrides:

printSubNodes in class QueryTreeNode

Parameters:

depth - The depth of this node in the tree

getResultSet

public ResultSetNode getResultSet()

Return the resultSet for this SubqueryNode.

Returns:

ResultSetNode underlying this SubqueryNode.

setResultSet

public void setResultSet(ResultSetNode resultSet)

getSubqueryType

public SubqueryNode.SubqueryType getSubqueryType()

Return the type of this subquery.

Returns:

int Type of this subquery.

setSubqueryType

public void setSubqueryType(SubqueryNode.SubqueryType subqueryType)

Set the type of this subquery.

Parameters:

subqueryType - of this subquery.

isEquivalent

protected boolean isEquivalent(ValueNode o)

Tests if this node is equivalent to the specified ValueNode. Two ValueNodes are considered equivalent if they will evaluate to the same value during query execution.

This method provides basic expression matching facility for the derived class of ValueNode and it is used by the language layer to compare the node structural form of the two expressions for equivalence at bind phase.

Note that it is not comparing the actual row values at runtime to produce a result; hence, when comparing SQL NULLs, they are considered to be equivalent and not unknown.

One usage case of this method in this context is to compare the select column expression against the group by expression to check if they are equivalent. e.g.:

SELECT c1+c2 FROM t1 GROUP BY c1+c2

In general, node equivalence is determined by the derived class of ValueNode. But they generally abide to the rules below:

• The two ValueNodes must be of the same node type to be considered equivalent. e.g.: CastNode vs. CastNode - equivalent (if their args also match), ColumnReference vs CastNode - not equivalent.
• If node P contains other ValueNode(s) and so on, those node(s) must also be of the same node type to be considered equivalent.
• If node P takes a parameter list, then the number of arguments and its arguments for the two nodes must also match to be considered equivalent. e.g.: CAST(c1 as INTEGER) vs CAST(c1 as SMALLINT), they are not equivalent.
• When comparing SQL NULLs in this context, they are considered to be equivalent.
• If this does not apply or it is determined that the two nodes are not equivalent then the derived class of this method should return false; otherwise, return true.

Specified by:

isEquivalent in class ValueNode

Parameters:

o - the node to compare this ValueNode against.

Returns:

true if the two nodes are equivalent, false otherwise.

getOrderByList

public OrderByList getOrderByList()

Get ORDER BY list (used to construct FROM only), cf. FromSubquery, for which this node is transient.

Returns:

order by list if specified, else null.

getOffset

public ValueNode getOffset()

Get OFFSET (used to construct FROM only), cf. FromSubquery, for which this node is transient.

Returns:

offset if specified, else null.

getFetchFirst

public ValueNode getFetchFirst()

Get FETCH FIRST (used to construct FROM only), cf. FromSubquery, for which this node is transient.

Returns:

fetch first if specified, else null.

getLeftOperand

public ValueNode getLeftOperand()