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a Java JDBC driver for reading comma-separated-value files

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/*
 *  CsvJdbc - a JDBC driver for CSV files
 *  Copyright (C) 2014 Simon Chenery
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2.1 of the License, or (at your option) any later version.
 *
 *  This library 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
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 */
package org.relique.jdbc.csv;

import java.sql.SQLException;
import java.util.LinkedList;
import java.util.List;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

class SQLCoalesceFunction extends Expression
{
	List expressions;
	public SQLCoalesceFunction(List expressions)
	{
		this.expressions = expressions;
	}
	@Override
	public Object eval(Map env) throws SQLException
	{
		Object retval = null;

		/*
		 * Find first expression that does not evaluate to NULL.
		 */
		Iterator it = expressions.iterator();
		while (retval == null && it.hasNext())
		{
			Expression expr = it.next();
			retval = expr.eval(env);
		}
		return retval;
	}
	@Override
	public String toString()
	{
		StringBuilder sb = new StringBuilder("COALESCE(");
		String delimiter = "";
		Iterator it = expressions.iterator();
		while (it.hasNext())
		{
			sb.append(delimiter);
			sb.append(it.next().toString());
			delimiter = ",";
		}
		sb.append(")");
		return sb.toString();
	}
	@Override
	public List usedColumns(Set availableColumns)
	{
		List result = new LinkedList<>();
		Iterator it = expressions.iterator();
		while (it.hasNext())
		{
			result.addAll(it.next().usedColumns(availableColumns));
		}
		return result;
	}
	@Override
	public List aggregateFunctions()
	{
		List result = new LinkedList<>();
		Iterator it = expressions.iterator();
		while (it.hasNext())
		{
			result.addAll(it.next().aggregateFunctions());
		}
		return result;
	}
}