public RelDataType inferReturnType(SqlOperatorBinding opBinding) {
assert opBinding.getOperandCount() == 1;
final RelDataType multisetType = opBinding.getOperandType(0);
RelDataType componentType = multisetType.getComponentType();
assert componentType != null : "expected a multiset type: " + multisetType;
final RelDataTypeFactory typeFactory = opBinding.getTypeFactory();
final RelDataType type =
typeFactory.builder().add(SqlUtil.deriveAliasFromOrdinal(0), componentType).build();
return typeFactory.createMultisetType(type, -1);
}
