PDO:绑定参数和连接字符串之间的区别 [英] PDO: Difference between binding params and concatenating string

问题描述

我有这个奇怪的问题.为什么这两个实现返回不同的结果?

I have this weird problem. Why do these two implementations return different results?

    $db = DbBase::getInstance();
    $stmt = $db->prepare('SELECT round(round(9.50 * :amount, 2) * 23 * 0.01, 2)');
    $stmt->execute(array(':amount' => 1));
    echo $stmt->fetchColumn();

    Result: 2.18

    $db = DbBase::getInstance();
    $stmt = $db->prepare('SELECT round(round(9.50 * 1, 2) * 23 * 0.01, 2)');
    $stmt->execute();
    echo $stmt->fetchColumn();

    Result: 2.19

当我绑定金额时，它会给我不同的结果.由于SQL注入，我宁愿不连接字符串.

When I bind the amount it gives me different result. I'd rather not concatenate the string because of the SQL injections.

推荐答案

使用数组传递数据时，数据将作为字符串传递:

When you are using the array to pass the data, the data is passed as a string:

从文档:

一个值数组，其中元素的数量与正在执行的SQL语句中绑定的参数一样多.所有值都视为PDO :: PARAM_STR.

An array of values with as many elements as there are bound parameters in the SQL statement being executed. All values are treated as PDO::PARAM_STR.

但是，当您直接在查询中手动输入1时，它将被视为一个int.让我看看是否可以做进一步的挖掘，以了解将字符串转换为int时内部发生的情况.

However, when you are manually entering in the 1 into the query directly it is being treated as an int. Let me see if I can do some further digging to see what happens internally when a string is converted into an int for you.

这可能是最相似的错误之一.提交并接受:

This is probably one of the most similar bugs that have been submitted and accepted:

1)
SET @a = 1;
SELECT @a;

2)
SET @a = 1.1;
SELECT @a;

.. and this 

3)
SET @a = 1.1;
SELECT @a + 7;
returns '8.100000000000000000000000000000'
(probably the addition will convert "1.1" to a double, the result 
of the addition is also a DOUBLE and finally the DOUBLE is converted 
to a string - that should be OK as well as far as I can understand)

因此，当您将int传递给mysql时，它似乎在内部将mysql转换为double.那会很好地解释您所看到的行为.

So it looks like internally mysql is converting to a double when you pass it an int. That would explain rather nicely the behavior that you are seeing.

以下是您可能感兴趣的其他类似(错误编号)错误的列表:

Here is a list of other similar (numbers not quite right) bugs you might be interested in:

http://bugs.mysql.com/bug.php?id=46037

http://bugs.mysql.com/bug.php?id=35071

http://bugs.mysql.com/bug.php?id=35071 <-表现出Win和Lin之间差异的好人

http://bugs.mysql.com/bug.php?id=35071 <-- Good one showing difference between Win and Lin

和

And a filtered list of data type bugs that I perused which make for interesting reading.

啊哈！

这是一个非常完美的错误解释了您的问题:

Here is a bug that rather perfectly explains your issue:

Reproduce code:
---------------
CREATE TABLE my_db.my_table (
  id int(10) unsigned NOT NULL auto_increment,
  PRIMARY KEY (id)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

<?php
$DB = new PDO('mysql:dbname=my_db;host=localhost', 'user', 'pass');
$stmt = $DB->prepare('select * from my_table where id>?');
$stmt->bindValue(1, 13);
$stmt->execute();
?>

or

<?php
$DB = new PDO('mysql:dbname=my_db;host=localhost', 'user', 'pass');
$stmt = $DB->prepare('select * from my_table where id>?');
$stmt->execute(array(13));
?>

Expected result:
----------------
select * from my_table where id>13

Actual result:
--------------
select * from my_table where id>'13'

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