mysql_fetch_field()

(PHP 4, PHP 5)

从结果集中取得列信息并作为对象返回

说明

mysql_fetch_field(resource $result[,int $field_offset]): object

返回一个包含字段信息的对象。

mysql_fetch_field()可以用来从某个查询结果中取得字段的信息。如果没有指定字段偏移量，则下一个尚未被mysql_fetch_field()取得的字段被提取。

对象的属性为：

• name -列名
• table -该列所在的表名
• max_length -该列最大长度
• not_null - 1，如果该列不能为NULL
• primary_key - 1，如果该列是 primary key
• unique_key - 1，如果该列是 unique key
• multiple_key - 1，如果该列是 non-unique key
• numeric - 1，如果该列是 numeric
• blob - 1，如果该列是 BLOB
• type -该列的类型
• unsigned - 1，如果该列是无符号数
• zerofill - 1，如果该列是 zero-filled

Note:此函数返回的字段名大小写敏感。

Example #1 mysql_fetch_field()

<?php
mysql_connect('localhost:3306', $user, $password)
    or die("Could not connect: " . mysql_error());
mysql_select_db("database");
$result = mysql_query("select * from table")
    or die("Query failed: " . mysql_error());
/* get column metadata */
$i = 0;
while ($i < mysql_num_fields($result)) {
    echo "Information for column $i:<br />\n";
    $meta = mysql_fetch_field($result);
    if (!$meta) {
        echo "No information available<br />\n";
    }
    echo "<pre>
blob:         $meta->blob
max_length:   $meta->max_length
multiple_key: $meta->multiple_key
name:         $meta->name
not_null:     $meta->not_null
numeric:      $meta->numeric
primary_key:  $meta->primary_key
table:        $meta->table
type:         $meta->type
unique_key:   $meta->unique_key
unsigned:     $meta->unsigned
zerofill:     $meta->zerofill
</pre>";
    $i++;
}
mysql_free_result($result);
?>

参见mysql_field_seek()。

参数

$result

resource型的结果集。此结果集来自对mysql_query()的调用。

$field_offset

The numerical field offset. If the field offset is not specified, the next field that was not yet retrieved by this function is retrieved. The$field_offsetstarts at0.

返回值

Returns an object containing field information. The properties of the object are:

• name - column name
• table - name of the table the column belongs to
• max_length - maximum length of the column
• not_null - 1 if the column cannot be NULL
• primary_key - 1 if the column is a primary key
• unique_key - 1 if the column is a unique key
• multiple_key - 1 if the column is a non-unique key
• numeric - 1 if the column is numeric
• blob - 1 if the column is a BLOB
• type - the type of the column
• unsigned - 1 if the column is unsigned
• zerofill - 1 if the column is zero-filled

范例

Example #2 mysql_fetch_field() example

<?php
$conn = mysql_connect('localhost', 'mysql_user', 'mysql_password');
if (!$conn) {
    die('Could not connect: ' . mysql_error());
}
mysql_select_db('database');
$result = mysql_query('select * from table');
if (!$result) {
    die('Query failed: ' . mysql_error());
}
/* get column metadata */
$i = 0;
while ($i < mysql_num_fields($result)) {
    echo "Information for column $i:<br />\n";
    $meta = mysql_fetch_field($result, $i);
    if (!$meta) {
        echo "No information available<br />\n";
    }
    echo "<pre>
blob:         $meta->blob
max_length:   $meta->max_length
multiple_key: $meta->multiple_key
name:         $meta->name
not_null:     $meta->not_null
numeric:      $meta->numeric
primary_key:  $meta->primary_key
table:        $meta->table
type:         $meta->type
unique_key:   $meta->unique_key
unsigned:     $meta->unsigned
zerofill:     $meta->zerofill
</pre>";
    $i++;
}
mysql_free_result($result);
?>

注释

Note:此函数返回的字段名大小写敏感。

参见

• mysql_field_seek()将结果集中的指针设定为制定的字段偏移量

It should be noted that the primary_key member variable is only set to 1 if the primary key on the table is only on that 1 field. If you have a table that has a multiple column primary key, then you will not get what you might expect.
For example:
CREATE TABLE `line_item_table` (
 `liForeignKey1` int(11) unsigned not null,
 `liForeignKey2` int(11) unsigned not null,
 PRIMARY KEY (`liForeignKey1`, `liForeignKey2`)
) ENGINE=MyISAM;
While you might expect that primary_key == 1 for both columns; var_dump() will show you that you get the following for both fields:
["primary_key"]=>int(0)
This is as of PHP 5.2.13 and MySQL 5.0.51

XML generation.
Bit of a security risk allowing parameters to select db and table on live server (unless user is restricted or replace the $_GET with fixed value.)
Outputs xml with standard format for <config> part to generate forms in flash.
<?php
  //
  //  makeXML.php?db=dbname&table=tablename
  //
  
  set_time_limit(300);
    
  $host = "localhost";
  $user = "root";
  $password = "root";
  
  $database = $_GET['db'];  
  $table = $_GET['table'];
  
  mysql_connect($host,$user,$password);
  @mysql_select_db($database) or die( "Unable to select database");
  
  $querytext="SELECT * FROM ".$table; 
  $result=mysql_query($querytext);
  
  if ($result){
    $num=mysql_num_rows($result);
  }else{
    $num=0;
  }
  
?>
<?php 
  header('Content-Type: text/xml');
   echo "<?xml version='1.0'?>"; 
   
   if ($num > 0){
 ?>
<<?php echo $table?>>
  <config>
    <?php
      // Display number of fields
      echo "<numFields>".mysql_num_fields($result)."</numFields>";
      $i = 0;
      $primaryKey = "";
      $nameArray = array(); 
      $maxLengthArray = array(); 
      $typeArray = array(); 
      while ($i < mysql_num_fields($result)) {
        $meta = mysql_fetch_field($result, $i);
        $nameArray[$i] = $meta->name;
        $maxLengthArray[$i] = $meta->max_length;
        $typeArray[$i] = $meta->type;
        if ($meta->primary_key){
          $primaryKey = $meta->name;
        }
        $i++;
      }
      $i = 0;
      echo "<fieldNames>";
      while ($i < count($nameArray)) {
        echo "<field".$i.">".$nameArray[$i]."</field".$i.">";
        $i++;
      }
      echo "</fieldNames>";
      $i = 0;
      echo "<fieldMaxLength>";
      while ($i < count($maxLengthArray)) {
        echo "<field".$i.">".$maxLengthArray[$i]."</field".$i.">";
        $i++;
      }
      echo "</fieldMaxLength>";
      $i = 0;
      echo "<fieldType>";
      while ($i < count($typeArray)) {
        echo "<field".$i.">".$typeArray[$i]."</field".$i.">";
        $i++;
      }
      echo "</fieldType>";
    ?>
    <primaryKey><?php echo $primaryKey?></primaryKey>
    <numRecords><?php echo $num?></numRecords>
  </config>
<?php 
  $i=0;
  while ($i < $num) {
    $ID=mysql_result($result,$i,"ID");
    $value=mysql_result($result,$i,"value");
    $title=mysql_result($result,$i,"title");
    $description=mysql_result($result,$i,"description");
?>
  <row>
    <ID><?php echo $ID?></ID>
    <weighting><?php echo $value?></weighting>
    <title><?php echo $title?></title>
    <description><?php echo $description?></description>
  </row>
<?php 
    $i = $i + 1;
  } 
?>
</<?php echo $table?>>
<?php 
  } 
?>

If you want the fields in a table, a simple DESCRIBE query will work:
<?php
$query ="DESCRIBE Users";
$result = mysql_query($query);
echo "<ul>";
while($i = mysql_fetch_assoc($result))
   echo "<li>{$i['Field']}</li>";
echo "</ul>";
?>
Should do the trick.

A little function to help coders to distinct the tablename from a multiselect query where some fields has the same name in differents tables.
<?php
public function sql($sql) {
  $T_Return=array();
  $result=@mysql_query($sql);
  
  $i=0;
  while ($i < mysql_num_fields($result)) {      
    $fields[]=mysql_fetch_field($result, $i);
    $i++;
  }
  
  while ($row=mysql_fetch_row($result)) {        
    $new_row=array();
    for($i=0;$i<count($row); $i++) {
      $new_row[ $fields[$i]->table][$fields[$i]->name]=$row[$i];
    }
    $T_Return[]=$new_row;
  }
  
  return $T_Return;
}
?>

Be sure to note that $max_length is the length of the longest value for that field in the returned dataset, NOT the maximum length of data that column is designed to hold.

The field type returns what PHP classifies the data found in the field, not how it is stored in the database; use the following example to retrieve the MySQL information about the field....
<?php
$USERNAME = '';
$PASSWORD = '';
$DATABASE = '';
$TABLE_NAME = '';
mysql_connect('localhost', $USERNAME, $PASSWORD)
  or die ("Could not connect");
$result = mysql_query("SHOW FIELDS FROM $DATABASE.$TABLE_NAME");
$i = 0;
while ($row = mysql_fetch_array($result)) {
 echo $row['Field'] . ' ' . $row['Type'];
}
?>

Simple function to display all data in a query...
function dumpquery($query) {
  $numfields = mysql_num_fields($query);
  echo '<table border="1" bgcolor="white"><tr>';
  for ($i = 0; $i<$numfields; $i += 1) {
    $field = mysql_fetch_field($query, $i);
    echo '<th>' . $field->name . '</th>';
  }
  echo '</tr>';
  while ($fielddata = mysql_fetch_array($query)) {
    echo '<tr>';
    for ($i = 0; $i<$numfields; $i += 1) {
      $field = mysql_fetch_field($query, $i);
      echo '<td>' . $fielddata[$field->name] . '</td>';
    }
    echo '</tr>';
  }
  echo '</table>';  
}

Performance Notes!
I used this script for testing, the table has 26 colums.
<?php
$t_start = microtime(true);
$sql = mysql_query("SELECT * FROM `table` LIMIT 1") or trigger_error(mysql_error(), E_USER_WARNING);
for ($i = 0; $i < mysql_num_fields($sql); $i++) {
  $meta = mysql_fetch_field($sql, $i);
  echo "Information for column ".$meta->name.":\n";
  echo 
"\tblob:     $meta->blob
\tmax_length:  $meta->max_length
\tmultiple_key: $meta->multiple_key
\tname:     $meta->name
\tnot_null:   $meta->not_null
\tnumeric:   $meta->numeric
\tprimary_key: $meta->primary_key
\ttable:    $meta->table
\ttype:     $meta->type
\tunique_key:  $meta->unique_key
\tunsigned:   $meta->unsigned
\tzerofill:   $meta->zerofill
";
}
$t_stop = microtime(true);
$t_proc = $t_stop - $t_start;
echo "processing time query 1: ".number_format($t_proc * 1000, 3)." ms\n";
unset($t_start);
unset($t_stop);
unset($t_proc);
$t_start = microtime(true);
$sql = mysql_query("DESCRIBE `table`");
while ($res = mysql_fetch_array($sql, MYSQL_ASSOC)) {
  print_r($res);
}
$t_stop = microtime(true);
$t_proc = $t_stop - $t_start;
echo "processing time query 2: ".number_format($t_proc * 1000, 3)." ms\n";
?>
Query 1 => 0.444 ms
Query 2 => 1.146 ms
So for easy usage, Query 2 is advised... But if your a performance-geek, you should use Query 1.

An improvement on the earlier mysql_column_exists function.
<?php
function mysql_column_exists($table_name, $column_name, $link=false) {
  $result = @mysql_query("SHOW COLUMNS FROM $table_name LIKE '$column_name'", $link);
  return (mysql_num_rows($result) > 0);
}
?>

Using mysql_fetch_field you can produce a more robust version of mysql_fetch_assoc.
When querying 2 tables with the same field names, generally you would need to use mysql_fetch_row to get an integer key'ed array rather than an associated key'ed array. This is because fields of the same name in the second table will over-write the data returned from the first table.
However this simple function will insert the table name prior to the field name for the key and prevent cross-overs.
ie SELECT *, 'test' AS test 4 FROM table AS T_1, table AS T_2 WHERE T_1.a=T_2.b
could produce:
mysql_fetch_assoc() returns
array(
'index'=>2,
'a'=>'pear',
'b'=>'apple',
'test'=>'test',
4=>4
)
mysql_fetch_table_assoc() returns
array(
'T_1.index' =>1,
'T_1.a'=>'apple',
'T_1.b'=>'banana',
'T_2.index'=>2,
'T_2.a'=>'pear',
'T_2.b'=>'apple',
'test'=>'test',
4=>4
)
<?php
function mysql_fetch_table_assoc($resource)
{
  // function to get all data from a query, without over-writing the same field
  // by using the table name and the field name as the index
  
  // get data first
  $data=mysql_fetch_row($resource);
  if(!$data) return $data; // end of data
  
  // get field info
  $fields=array();
  $index=0;
  $num_fields=mysql_num_fields($resource);
  while($index<$num_fields)
  {
    $meta=mysql_fetch_field($resource, $index);
    if(!$meta)
    {
      // if no field info then just use index number by default
      $fields[$index]=$index;
    }
    else
    {
      $fields[$index]='';
      // deal with field aliases - ie no table name (SELECT T_1.a AS temp)
      if(!empty($meta->table)) $fields[$index]=$meta->table.'.';
      // deal with raw data - ie no field name (SELECT 1)
      if(!empty($meta->name)) $fields[$index].=$meta->name; else $fields[$index].=$index;
    }
    $index++;
  }
  $assoc_data=array_combine($fields, $data);
  return $assoc_data;
}
?>

I needed to get the field information and the enum/set values. Here is the function I created to expand the object returned by mysql_fetch_field. I also, decided to return all the fields for a table in an array of field objects by "name" and position much like mysql_fetch_array does.
You could test it by using:
<?php
$myfields = GetFieldInfo('test_table');
print "<pre>";
print_r($myfields);
print "</pre>";
?>
The field objects now have 'len', 'values' and 'flags' parameters. 
NOTE: 'values' only has data for set and enum fields.
<?php
//This assumes an open database connection
//I also use a constant DB_DB for current database.
function GetFieldInfo($table)
{
 if($table == '') return false;
 $fields = mysql_list_fields(DB_DB, $table);
 if($fields){
  $columns = mysql_query('show columns from ' . $table);
  if($columns){
   $num = mysql_num_fields($fields);
   for($i=0; $i < $num; ++$i){
    $column = mysql_fetch_array($columns);
    $field = mysql_fetch_field($fields, $i);
    $flags = mysql_field_flags($fields, $i);
    if($flags == '') $flags=array();
    else $flags = explode(' ',$flags);
    if (ereg('enum.(.*).',$column['Type'],$match))
     $field->values = explode(',',$match[1]);
    if (ereg('set.(.*).',$column['Type'],$match))
     $field->values = explode(',',$match[1]);
    if(!$field->values) $field->values = array();
    $field->flags = $flags;
    $field->len = mysql_field_len($fields, $i);
    $result_fields[$field->name] = $field;
    $result_fields[$i] = $field;
   }
   mysql_free_result($columns);
  }
  mysql_free_result($fields);
  return $result_fields;
 }
 return false;
}
?>
hope someone else finds this useful.

MYSQLI_TYPE_BLOB indicates the field is a BLOB or a TEXT. I think you would need to check the blob value. If its true then it's a BLOB, otherwise it's a TEXT. Can someone confirm?

Simple PHP script for displaying the field names. Presuming the database is seleected already.
<?php
$sql = "SELECT * FROM table_name;";
$result = mysql_query($sql);
$i = 0;
while($i<mysql_num_fields($result))
{
 $meta=mysql_fetch_field($result,$i);
 echo $i.".".$meta->name."<br />";
 $i++;
}
?>
OUTPUt:
0.id
1.todo
2.due date
3.priority
4.type
5.status
6.notes
hope this is useful.