ZDemo.java

/*
 * This file is part of Zql.
 *
 * Zql is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Zql is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Zql.  If not, see <http://www.gnu.org/licenses/>.
 */


import java.sql.SQLException;
import java.util.Vector;
import java.io.*;

import org.gibello.zql.*;

/**
 * <pre>
 * ZDemo is able to send SQL queries to simple CSV (comma-separated values)
 * files; the CSV syntax used here is very simple:
 *  The 1st line contains the column names
 *  Other lines contain column values (tuples)
 *  Values are separated by commas, so they can't contain commas (it's just
 *  for demo purposes).
 * Example:
 * Create a num.db text file that contains the following:
 *  a,b,c,d,e
 *  1,1,1,1,1
 *  2,2,2,2,2
 *  1,2,3,4,5
 *  5,4,3,2,1
 * You can then run ZDemo, and query it; some legal queries follow:
 *  select * from num;
 *  select a, b from num;
 *  select a+b, c from num;
 *  select * from num where a = 1 or e = 1;
 *  select * from num where a = 1 and b = 1 or e = 1;
 *  select d, e from num where a + b + c <= 3;
 *  select * from num where 3 = a + b + c;
 *  select * from num where a = b or e = d - 1;
 *  select * from num where b ** a <= 2;
 * </pre>
 */
public class ZDemo {

  public static void main(String args[]) {
    try {

      ZqlParser p = null;

      if(args.length < 1) {
        System.out.println("Reading SQL from stdin (quit; or exit; to quit)");
        p = new ZqlParser(System.in);
      } else {
        p = new ZqlParser(new DataInputStream(new FileInputStream(args[0])));
      }

      // Read all SQL statements from input
      ZStatement st;
      while((st = p.readStatement()) != null) {

        System.out.println(st.toString()); // Display the statement

        if(st instanceof ZQuery) { // An SQL query: query the DB
          queryDB((ZQuery)st);
        } else if(st instanceof ZInsert) { // An SQL insert
          insertDB((ZInsert)st);
        }
      }

    } catch(Exception e) {
      e.printStackTrace();
    }
  }

  /**
   * Query the database
   */
  static void queryDB(ZQuery q) throws Exception {

    Vector sel = q.getSelect(); // SELECT part of the query
    Vector from = q.getFrom();  // FROM part of the query
    ZExpression where = (ZExpression)q.getWhere();  // WHERE part of the query

    if(from.size() > 1) {
      throw new SQLException("Joins are not supported");
    }

    // Retrieve the table name in the FROM clause
    ZFromItem table = (ZFromItem)from.elementAt(0);

    // We suppose the data is in a text file called <tableName>.db
    // <tableName> is the table name in the FROM clause
    BufferedReader db = new BufferedReader(
      new FileReader(table.getTable() + ".db"));
    
    // Read the column names (the 1st line of the .db file)
    ZTuple tuple = new ZTuple(db.readLine()); 

    ZEval evaluator = new ZEval();

    // Now, each line in the .db file is a tuple
    String tpl;
    while((tpl = db.readLine()) != null) {

      tuple.setRow(tpl);

      // Evaluate the WHERE expression for the current tuple
      // Display the tuple if the condition evaluates to true

      if(where == null || evaluator.eval(tuple, where)) {
        DisplayTuple(tuple, sel);
      }

    }

    db.close();
  }

  /**
   * Display a tuple, according to a SELECT map
   */
  static void DisplayTuple(ZTuple tuple, Vector map) throws Exception {

    // If it is a "select *", display the whole tuple
    if(((ZSelectItem)map.elementAt(0)).isWildcard()) {
      System.out.println(tuple.toString());
      return;
    }

    ZEval evaluator = new ZEval();

    // Evaluate the value of each select item
    for(int i=0; i<map.size(); i++) {

      ZSelectItem item = (ZSelectItem)map.elementAt(i);
      System.out.print(
        evaluator.evalExpValue(tuple, item.getExpression()).toString());

      if(i == map.size()-1) System.out.println("");
      else System.out.print(", ");
    }
  }

  static void insertDB(ZInsert ins) throws Exception {
    System.out.println("Should implement INSERT here");
    System.out.println(ins.toString());
  }

};