@Override
    public void analyzeImpl(Analyzer analyzer) throws AnalysisException {
        desc = analyzer.registerVirtualColumnRef(super.getColumnName(), type, tupleDescriptor);
        numDistinctValues = desc.getStats().getNumDistinctValues();
    }
@Test
    public void analyzeImpl() {
        try {
            virtualSlot.analyzeImpl(analyzer);
        } catch (Exception e) {
            Assert.fail("analyze throw exception");
        }
    }