/**
* Returns whether a node represents the NULL value.
*
* <p>Examples:
*
* <ul>
* <li>For {@link org.eigenbase.rex.RexLiteral} Unknown, returns false.
* <li>For <code>CAST(NULL AS <i>type</i>)</code>, returns true if <code>
* allowCast</code> is true, false otherwise.
* <li>For <code>CAST(CAST(NULL AS <i>type</i>) AS <i>type</i>))</code>, returns false.
* </ul>
*/
public static boolean isNullLiteral(RexNode node, boolean allowCast) {
if (node instanceof RexLiteral) {
RexLiteral literal = (RexLiteral) node;
if (literal.getTypeName() == SqlTypeName.NULL) {
assert (null == literal.getValue());
return true;
} else {
// We don't regard UNKNOWN -- SqlLiteral(null,Boolean) -- as
// NULL.
return false;
}
}
if (allowCast) {
if (node.isA(RexKind.Cast)) {
RexCall call = (RexCall) node;
if (isNullLiteral(call.operands[0], false)) {
// node is "CAST(NULL as type)"
return true;
}
}
}
return false;
}
/**
* Returns whether a node represents the NULL value or a series of nested CAST(NULL as <TYPE>)
* calls<br>
* For Example:<br>
* isNull(CAST(CAST(NULL as INTEGER) AS VARCHAR(1))) returns true
*/
public static boolean isNull(RexNode node) {
/* Checks to see if the RexNode is null */
return RexLiteral.isNullLiteral(node)
|| ((node.getKind() == RexKind.Cast) && isNull(((RexCall) node).operands[0]));
}