columns.add(entry.getValue());
}
// introduce a projection to match the expected output
IdentityProjectionInfo mappings = computeIdentityMapping(symbols.build(), query.getLayout(), context.getTypes());
OperatorFactory sourceOperator = new FilterAndProjectOperatorFactory(context.getNextOperatorId(), FilterFunctions.TRUE_FUNCTION, mappings.getProjections());
PhysicalOperation source = new PhysicalOperation(sourceOperator, mappings.getOutputLayout(), query);
Symbol outputSymbol = Iterables.getOnlyElement(node.getOutputSymbols());
MaterializedViewWriterOperatorFactory operator = new MaterializedViewWriterOperatorFactory(
context.getNextOperatorId(),