pack-priv Class CurrentRowLocationNode

Overrides org.apache.derby.impl.sql.compile.ValueNode.bindExpression.

Binding this expression means setting the result DataTypeServices. In this case, the result type is always the same.

Parameters

fromList:FromList

The FROM list for the statement. This parameter is not used in this case.

subqueryList:SubqueryList

The subquery list being built as we find SubqueryNodes

aggregates:List<AggregateNode>

The aggregate list being built as we find AggregateNodes

Returns:ValueNode

The new top of the expression tree.

Annotations

@Override

Exceptions

StandardException:

Thrown on error

Overrides org.apache.derby.impl.sql.compile.ValueNode.generateExpression.

CurrentRowLocationNode is used in updates and deletes. See generate() in UpdateNode and DeleteNode to get the full overview of generate(). This class is responsible for generating the method that will return the RowLocation for the next row to be updated or deleted. This routine will generate a method of the form: private SQLRef fieldx; ... protected DataValueDescriptor exprx() throws StandardException { return fieldx = ( "result set member".getRowLocation(), fieldx); } and return the generated code: exprx() ("result set member" is a member of the generated class added by UpdateNode or DeleteNode.) This exprx function is used within another exprx function, and so doesn't need a static field or to be public; but at present, it has both. fieldx is a generated field that is initialized to null when the activation is constructed. getSQLRef will re-use fieldx on calls after the first call, rather than allocate a new SQLRef for each call.

Parameters

acb:ExpressionClassBuilder

The ExpressionClassBuilder for the class being built

mbex:MethodBuilder

Doc from org.apache.derby.impl.sql.compile.ValueNode.generateExpression.

The method the expression will go into

Annotations

@Override

Exceptions

StandardException:

Thrown on error

Implements abstract org.apache.derby.impl.sql.compile.ValueNode.isEquivalent.

Doc from org.apache.derby.impl.sql.compile.ValueNode.isEquivalent.

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.

Parameters

o:ValueNode

the node to compare this ValueNode against.

Returns:boolean

true if the two nodes are equivalent, false otherwise.