pack-priv Class BaseColumnNode

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

Doc from org.apache.derby.impl.sql.compile.QueryTreeNode.acceptChildren.

Accept a visitor on all child nodes. All sub-classes that add fields that should be visited, should override this method and call accept(v) on all visitable fields, as well as super.acceptChildren(v) to make sure all visitable fields defined by the super-class are accepted too.

Parameters

v:Visitor

the visitor

Annotations

@Override

Exceptions

StandardException:

on errors raised by the visitor

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

Do the code generation for this node. Should never be called.

Parameters

acb:ExpressionClassBuilder

The ExpressionClassBuilder for the class being built

mb:MethodBuilder

The method the code to place the code

Annotations

@Override

Exceptions

StandardException:

Thrown on error

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

Get the name of this column

Returns:String

The name of this column

Annotations

@Override

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

Get the user-supplied schema name for this column's table. This will be null if the user did not supply a name (for example, select t.a from t). Another example for null return value (for example, select b.a from t as b). But for following query select app.t.a from t, this will return APP

Returns:String

The schema name for this column's table

Annotations

@Override

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

Get the user-supplied table name of this column. This will be null if the user did not supply a name (for example, select a from t). The method will return B for this example, select b.a from t as b The method will return T for this example, select t.a from t

Returns:String

The user-supplied name of this column. Null if no user- supplied name.

Annotations

@Override

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.