mysqli_fetch_fields()
的length
结果给了我不准确的结果。
MySQL> DESCRIBE Notices;
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)
然而
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);
生成以下输出:
// 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
)
)
如果您查看,您会发现报告的CHAR
字段长度不匹配。 DESCRIBE
给了我255
,而fetch_fields()
给了我765
。为什么?
(如果您想知道,这个想法是为<input>
标签生成一个maxlength
属性。
字段长度为 255 个字符,但报告的长度以字节为单位。
由于 MySQL 对 UTF-8 排序规则的每个字符使用 3 个字节,因此您将获得 255*3 = 765
作为结果。
mysqli_result::fetch_fields()
/mysqli_fetch_fields()
输出中的length
和charsetnr
值显然取决于客户端定义的默认字符集。
例如,33
的charsetnr
代表 UTF-8。准确地说,它实际上代表字符集"utf8"的排序规则"utf8_general_ci"。可以通过执行此查询来检索该信息:
SELECT * FROM information_schema.collations;
可以通过以下查询检索可用字符集及其字符长度的列表:
SELECT * FROM information_schema.character_sets;
默认客户端字符集可以通过 PHP 调用 mysqli::set_charset()
/mysqli_set_charset()
来更改。
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错误 68573 中。
默认字符集也可以在服务器配置中定义,如另一个线程中所述。
由于fetch_fields()
的这种行为非常令人困惑,我要求在错误 68574 中更改它。
我将结果除法:
$result = mysqli_query($con,"SELECT * from tabla");
$campoTD = mysqli_fetch_fields($result);
foreach ($campoTD as $campo){
echo '<input maxlength='.number_format($campo[$i]->length / 3).' >';
$i++;
}
我遇到了同样的问题,发现你需要使用:$val>长度;
不是max_length,max_length是该特定列中值的最大长度,而不是表 def。
如果要使用表定义,请使用"长度"。
$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