Method processExpression

src/java/simpledb/Parser.java:51–138

(TransactionId tid, ZExpression wx, LogicalPlan lp)

    }

    void processExpression(TransactionId tid, ZExpression wx, LogicalPlan lp)
            throws simpledb.ParsingException, IOException, ParseException {
        if (wx.getOperator().equals("AND")) {
            for (int i = 0; i < wx.nbOperands(); i++) {
                if (!(wx.getOperand(i) instanceof ZExpression)) {
                    throw new simpledb.ParsingException(
                            "Nested queries are currently unsupported.");
                }
                ZExpression newWx = (ZExpression) wx.getOperand(i);
                processExpression(tid, newWx, lp);

            }
        } else if (wx.getOperator().equals("OR")) {
            throw new simpledb.ParsingException(
                    "OR expressions currently unsupported.");
        } else {
            // this is a binary expression comparing two constants
            @SuppressWarnings("unchecked")
            List<ZExp> ops = wx.getOperands();
            if (ops.size() != 2) {
                throw new simpledb.ParsingException(
                        "Only simple binary expresssions of the form A op B are currently supported.");
            }

            boolean isJoin = false;
            Predicate.Op op = getOp(wx.getOperator());

            boolean op1const = ops.get(0) instanceof ZConstant; // otherwise
                                                                      // is a
                                                                      // Query
            boolean op2const = ops.get(1) instanceof ZConstant; // otherwise
                                                                      // is a
                                                                      // Query
            if (op1const && op2const) {
                isJoin = ((ZConstant) ops.get(0)).getType() == ZConstant.COLUMNNAME
                        && ((ZConstant) ops.get(1)).getType() == ZConstant.COLUMNNAME;
            } else if (ops.get(0) instanceof ZQuery
                    || ops.get(1) instanceof ZQuery) {
                isJoin = true;
            } else if (ops.get(0) instanceof ZExpression
                    || ops.get(1) instanceof ZExpression) {
                throw new simpledb.ParsingException(
                        "Only simple binary expresssions of the form A op B are currently supported, where A or B are fields, constants, or subqueries.");
            } else
                isJoin = false;

            if (isJoin) { // join node

                String tab1field = "", tab2field = "";

                if (!op1const) { // left op is a nested query
                    // generate a virtual table for the left op
                    // this isn't a valid ZQL query
                } else {
                    tab1field = ((ZConstant) ops.get(0)).getValue();

                }