@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		ColumnsReference other = (ColumnsReference) obj;
		if (columnNames == null) {
			if (other.columnNames != null)
				return false;
		} else if (!columnNames.equals(other.columnNames))
			return false;
		if (tableName == null) {
			if (other.tableName != null)
				return false;
		} else if (!tableName.equals(other.tableName))
			return false;
		return true;
	}