查询过程前面解析类似insert，最终调用是在下面这个QuerySpecification类的getSingleResult方法，RangeVariable是查询条件相关

  private Result getSingleResult(Session session, int maxRows) {

        int[] limits = sortAndSlice.getLimits(session, this, maxRows);
        Result              r         = buildResult(session, limits);
        RowSetNavigatorData navigator = (RowSetNavigatorData) r.getNavigator();

        if (isDistinctSelect) {
            navigator.removeDuplicates(session);
        }

        if (sortAndSlice.hasOrder()) {
            navigator.sortOrder(session);
        }

        if (limits != SortAndSlice.defaultLimits
                && !sortAndSlice.skipFullResult) {
            navigator.trim(limits[0], limits[1]);
        }

        return r;
    }

    private Result buildResult(Session session, int[] limits) {

        RowSetNavigatorData navigator = new RowSetNavigatorData(session,
            (QuerySpecification) this);
        Result result = Result.newResult(navigator);

        result.metaData = resultMetaData;

        if (isUpdatable) {
            result.rsProperties = ResultProperties.updatablePropsValue;
        }

        int skipCount  = 0;
        int limitCount = limits[2];

        if (sortAndSlice.skipFullResult) {
            skipCount  = limits[0];
            limitCount = limits[1];
        }

        if (this.isSimpleCount) {
            Object[] data  = new Object[indexLimitData];
            Table    table = rangeVariables[0].getTable();

            table.materialise(session);

            PersistentStore store = table.getRowStore(session);
            long            count = store.elementCount(session);

            data[0] = data[indexStartAggregates] = ValuePool.getLong(count);

            navigator.add(data);

            return result;
        }

        int fullJoinIndex = 0;
        RangeIterator[] rangeIterators =
            new RangeIterator[rangeVariables.length];

        for (int i = 0; i < rangeVariables.length; i++) {
            rangeIterators[i] = rangeVariables[i].getIterator(session);
        }

        session.sessionContext.rownum = 1;

        for (int currentIndex = 0; ; ) {
            if (currentIndex < fullJoinIndex) {

                // finished current span
                // or finished outer rows on right navigator
                boolean end = true;

                for (int i = fullJoinIndex + 1; i < rangeVariables.length;
                        i++) {
                    if (rangeVariables[i].isRightJoin) {
                        fullJoinIndex = i;
                        currentIndex  = i;
                        end           = false;

                        ((RangeIteratorRight) rangeIterators[i])
                            .setOnOuterRows();

                        break;
                    }
                }

                if (end) {
                    break;
                }
            }

            RangeIterator it = rangeIterators[currentIndex];

            if (it.next()) {
                if (currentIndex < rangeVariables.length - 1) {
                    currentIndex++;

                    continue;
                }
            }