如何处理ResultSet，你知道它只有一个记录(How to process ResultSet you know has only one record in it)

 我正在努力完成一项家庭作业，并且我正忙着处理一些SQL查询。 
 
 我的查询是询问库存数据库中某个项目的数量。 在给定主键的情况下，查询从表中请求名为quantity_in_stock的列。 
 
 我已经初步化了一些准备好的陈述。 这是我在这里使用的那个： 
 
stmtFindColumn = Database.getConnection().prepareStatement(String.format("select ? from %s where %s = ?",
            INVENTORY_TABLE_NAME, SKU) );
 
 现在调用一个单独的方法。 我传递一个静态const QTY_IN_STOCK，它定义为“quantity_in_stock”和项目的SKU编号，它是表中的主键。 
 
private int getIntegerFromTable(String column, String key) {

    int toReturn = 0;

    try {
        // Complete the prepared statement 
        stmtFindColumn.setString(1, column);
        stmtFindColumn.setString(2, key);

        ResultSet result = stmtFindColumn.executeQuery();               
        toReturn = result.getInt(column);

    } catch (SQLException e) {
        LOG.error(e.getMessage());
        e.printStackTrace();
    }
    return toReturn;
}
 
 当我运行查询时，我得到一个sql异常，告诉我：无效的列名称quantity_in_stock。 
 
 我尝试使用while循环处理result.next（）并得到相同的错误。 当您知道只返回一条记录时，我找不到任何关于如何正确获取结果的示例。 
 
 帮帮我！ 
 
 编辑：好的，我发现我的部分问题是我没有得到结果集，我应该期待一个。 有任何想法吗？ 
 
 更新：我已经测试了我的代码，使用了一个花园变量语句和一个普通的字符串查询，它工作得很好。 所以问题在于我使用了准备好的声明。 有人可以检查我是否正在使用？ 通配符正确吗？ 谢谢！ 

I'm struggling with a homework assignment and am getting hung up on some SQL queries.
 
My query is interrogating an inventory database for the quantity of some item. The query requests the column with the name quantity_in_stock from the table, given the primary key.
 
I have initialized some prepared statements. This is the one I'm using here:
 
stmtFindColumn = Database.getConnection().prepareStatement(String.format("select ? from %s where %s = ?",
            INVENTORY_TABLE_NAME, SKU) );
 
Now a separate method is called. I pass it a static const QTY_IN_STOCK, which is defined as "quantity_in_stock" and the item's SKU number, which is the primary key in the table.
 
private int getIntegerFromTable(String column, String key) {

    int toReturn = 0;

    try {
        // Complete the prepared statement 
        stmtFindColumn.setString(1, column);
        stmtFindColumn.setString(2, key);

        ResultSet result = stmtFindColumn.executeQuery();               
        toReturn = result.getInt(column);

    } catch (SQLException e) {
        LOG.error(e.getMessage());
        e.printStackTrace();
    }
    return toReturn;
}
 
When I run the query I get an sql exception that tells me: Invalid column name quantity_in_stock.
 
I have tried using a while loop processing result.next() and get the same error. I can't find any examples of how to properly get the results when you know only a single record is being returned.
 
Help!
 
EDIT: OK, I've found that part of my problem is I'm not getting a result set, where I should expect one. Any ideas?
 
UPDATE: I've tested my code, using a garden variety statement and a plain string query instead and it works just fine. So the problem is in my use of the prepared statement. Can someone check if I'm using the ? wildcards correctly? Thanks!

原文：https://stackoverflow.com/questions/8283786