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/*
 * 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 .
 */

package net.sf.mongodb_jdbc_driver.zql;

/**
 * ZSelectItem: an item in the SELECT part of an SQL query. (The SELECT part of a query is a Vector of
 * ZSelectItem).
 */
public class ZSelectItem extends ZAliasedName
{

	private static final long serialVersionUID = 678532087449466687L;

	ZExp expression_ = null;

	String aggregate_ = null;

	/**
	 * Create a new SELECT item
	 */
	public ZSelectItem()
	{
		super();
	}

	/**
	 * Create a new SELECT item, given its name (for column names and wildcards).
	 * 
	 * @param fullname
	 *           A string that represents a column name or wildcard (example: a.*).
	 */
	public ZSelectItem(String fullname)
	{
		super(fullname, ZAliasedName.FORM_COLUMN);
		setAggregate(ZUtils.getAggregateCall(fullname)); // PY.Gibello 21 Apr 2001
	}

	/**
	 * @return An SQL Expression if this SELECT item is an expression, a ZConstant if it is a column name, null
	 *         if it is a wildcard
	 */
	public ZExp getExpression()
	{
		if (isExpression()) return expression_;
		else if (isWildcard()) return null;
		else
		{
			return new ZConstant(getColumn(), ZConstant.COLUMNNAME);
		}
	}

	/**
	 * Initialize this SELECT item as an SQL expression (not a column name nor wildcard) Example: SELECT a+b
	 * FROM table1; (a+b is an expression)
	 */
	public void setExpression(ZExp e)
	{
		expression_ = e;
		strform_ = expression_.toString();
	}

	/**
	 * @return true if this item is an SQL expression, false if not. (Example: SELECT a+b, c FROM num; -> a+b
	 *         is an expression, not c)
	 */
	public boolean isExpression()
	{
		return (expression_ != null && expression_ instanceof ZExpression);
	}

	/**
	 * Initialize an aggregate function on this item (generally SUM, AVG, MAX, MIN) Example: SELECT AVG(age)
	 * FROM people; -> The aggregate function is AVG.
	 * 
	 * @param a
	 *           The name of the aggregate function (a String, like SUM, AVG, MAX, MIN)
	 */
	public void setAggregate(String a)
	{
		aggregate_ = a;
	}

	/**
	 * If this item is an aggregate function, return the function name.
	 * 
	 * @return The name of an aggregate function (generally SUM, AVG, MAX, MIN), or null if there's no
	 *         aggregate. Example: SELECT name, AVG(age) FROM people; -> null for the "name" item, and "AVG"
	 *         for the "AVG(age)" item.
	 */
	public String getAggregate()
	{
		return aggregate_;
	}

	/**
	 * TBD public String toString() { String agg = getAggregate(); if(agg == null) agg = ""; return agg +
	 * super.toString(); }
	 **/
};