MySQL将一行乘以一个变量

我试图将一行乘以一个变量（计算量）：

计算“servingsMultiplier”和“servingSizeMultiplier”的值

当我使用一个常数（例如，2）时，上述方法有效；但是，当我使用变量时，情况并非如此。我收到错误消息：

“recipePDF中的SQLException: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException:未知 “字段列表”中的“servingsMultiplier”列

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如果要使用mysql变量，请在变量名之前添加

@

SELECT ci_id, cr_id, ci_ingedient, (ci_amount*@servingsMultiplier) AS ci_amount,
(ci_unit*@servingSizeMultiplier) AS ci_unit
FROM at_cat_ingredient 
WHERE cr_id = @id
ORDER BY ci_ingedient;

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sql语句中的标识符（如

servingsMultiplier

）不会被识别为变量的值，而是作为列名，当然，列名并不存在。
在语句中使用

？

占位符作为

servingsMultiplier

和

servingSizeMultiplier

的占位符，并传递它们的值，就像传递

WHERE

子句中的参数一样：

String selectQry5 = 
    "SELECT ci_id, cr_id, ci_ingedient, " + 
    "(ci_amount * ?) AS ci_amount, " + 
    "(ci_unit * ?) AS ci_unit " +
    "FROM at_cat_ingredient " + 
    "WHERE cr_id = ? " +
    "ORDER BY ci_ingedient;";

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这是某种应用程序代码

SELECT ci_id, cr_id, ci_ingedient, (ci_amount*@servingsMultiplier) AS ci_amount,
(ci_unit*@servingSizeMultiplier) AS ci_unit
FROM at_cat_ingredient 
WHERE cr_id = @id
ORDER BY ci_ingedient;

String selectQry5 = 
    "SELECT ci_id, cr_id, ci_ingedient, " + 
    "(ci_amount * ?) AS ci_amount, " + 
    "(ci_unit * ?) AS ci_unit " +
    "FROM at_cat_ingredient " + 
    "WHERE cr_id = ? " +
    "ORDER BY ci_ingedient;";