Question

length的{{1}}结果给了我不准确的结果。

MySQL＆gt; mysqli_fetch_fields()

DESCRIBE Notices;

然而，

Field     Type               Null     Key     Default     Extra
Id        int(10) unsigned   NO       PRI     (NULL)      auto_increment
UserId    int(10) unsigned   NO       MUL     (NULL)
Title     char(255)          NO               (NULL)
Name      char(255)          NO               (NULL)
Summary   text               NO               (NULL)

产生以下输出：

class Db {
    public function exec($sql) {
        if (!$this->link) {
            $this->open();
        }
        if (($this->result = mysqli_query($this->link, $sql)) === false) {
            throw new Exception('<b>' . __METHOD__ . '</b>: ' . $sql . ': ' . mysqli_error($this->link));
        }
        return true;
    }
    public function field_info($table) {
        $sql = 'SELECT * FROM `' . $table . '` LIMIT 1';
        $this->exec($sql);
        return $this->field_info = $this->result->fetch_fields();
    }
}

$a  = $db->field_info('Notices');
print_r($a);

如果你看，你会发现// Note: "max_length" is the maximum existing length in the result set, // while "length" is the set maximum length in the table definition. Array ( [0] => stdClass Object ( [name] => Id [orgname] => Id [table] => Notices [orgtable] => Notices [def] => [max_length] => 1 [length] => 10 [charsetnr] => 63 [flags] => 49699 [type] => 3 [decimals] => 0 ) [1] => stdClass Object ( [name] => UserId [orgname] => UserId [table] => Notices [orgtable] => Notices [def] => [max_length] => 1 [length] => 10 [charsetnr] => 63 [flags] => 53289 [type] => 3 [decimals] => 0 ) [2] => stdClass Object ( [name] => Title [orgname] => Title [table] => Notices [orgtable] => Notices [def] => [max_length] => 27 [length] => 765 [charsetnr] => 33 [flags] => 4097 [type] => 254 [decimals] => 0 ) [3] => stdClass Object ( [name] => Name [orgname] => Name [table] => Notices [orgtable] => Notices [def] => [max_length] => 25 [length] => 765 [charsetnr] => 33 [flags] => 4097 [type] => 254 [decimals] => 0 ) [4] => stdClass Object ( [name] => Summary [orgname] => Summary [table] => Notices [orgtable] => Notices [def] => [max_length] => 26 [length] => 196605 [charsetnr] => 33 [flags] => 4113 [type] => 252 [decimals] => 0 ) )字段的报告长度不匹配。 CHAR正在给我DESCRIBE，而255正在给我fetch_fields()。为什么呢？

（如果您想知道，这个想法是为765代码生成maxlength属性。）

Answer 1

您的字段长度为255 字符，但报告的长度为字节。

由于MySQL使用3 bytes per character进行UTF-8排序规则，因此结果会得到255 * 3 = 765。

Answer 2

length / charsetnr输出中的mysqli_result::fetch_fields()以及mysqli_fetch_fields()值显然取决于客户端定义的默认字符集。

E.g。 charsetnr代表33代表UTF-8。确切地说，它实际上代表整理＆＃39; utf8_general_ci＆＃39;字符集＆＃39; utf8＆＃39;。可以通过执行以下查询来检索该信息：

SELECT * FROM information_schema.collations;

可以通过此查询检索可用字符集列表及其字符长度：

SELECT * FROM information_schema.character_sets;

可以通过PHP调用mysqli::set_charset() / mysqli_set_charset()来更改默认客户端字符集。

示例：

$dbHandle->set_charset('latin1');

mysqli_fetch_fields()的PHP文档目前不包含该信息，因此我请求将其添加到bug 68573。

默认字符集也可以是defined within the server configuration described in another thread。

由于fetch_fields()的这种行为非常混乱，我请求在bug 68574更改它。

Answer 3

我将结果分开：

$result = mysqli_query($con,"SELECT * from tabla");
$campoTD = mysqli_fetch_fields($result);
  foreach ($campoTD as $campo){
    echo '<input maxlength='.number_format($campo[$i]->length / 3).' >';
    $i++;
  }

Answer 4

我遇到了同样的问题，发现你需要使用： $ val-＆GT;长度;

不是max_length，max_length是特定列中值的最大长度，而不是表def。

如果您希望表定义使用'length'。

$q = $mysqli->query("select * from table");

$finfo = $q->fetch_fields();

foreach ($finfo as $val) {

    echo $val->length;

}

参考：http://php.undmedlibrary.org/manual/de/function.mysqli-fetch-fields.php

为什么mysqli_fetch_fields（）给我不准确的结果？

4 个答案: