mysqli_result::fetch_fields()

(PHP 5, PHP 7)

Returns an array of objects representing the fields in a result set

说明

面向对象风格
mysqli_result::fetch_fields(void): array

过程化风格
mysqli_fetch_fields(mysqli_result$result): array

This function serves an identical purpose to the mysqli_fetch_field() function with the single difference that, instead of returning one object at a time for each field, the columns are returned as an array of objects.

参数

$result: 仅以过程化样式：由mysqli_query()，mysqli_store_result()或mysqli_use_result()返回的结果集标识。

返回值

Returns an array of objects which contains field definition information or FALSE if no field information is available.

**Object properties**
Property	Description
name	The name of the column
orgname	Original column name if an alias was specified
table	The name of the table this field belongs to(if not calculated)
orgtable	Original table name if an alias was specified
max_length	The maximum width of the field for the result set.
length	The width of the field, in bytes, as specified in the table definition. Note that this number(bytes)might differ from your table definition value(characters), depending on the character set you use. For example, the character set utf8 has 3 bytes per character, so varchar(10)will return a length of 30 for utf8(103), but return 10 for latin1(101).
charsetnr	The character set number(id)for the field.
flags	An integer representing the bit-flags for the field.
type	The data type used for this field
decimals	The number of decimals used(for integer fields)

范例

Example #1 面向对象风格

<?php
$mysqli = new mysqli("127.0.0.1", "root", "foofoo", "sakila");
/* check connection */
if ($mysqli->connect_errno) {
    printf("Connect failed: %s\n", $mysqli->connect_error);
    exit();
}
foreach (array('latin1', 'utf8') as $charset) {
    // Set character set, to show its impact on some values (e.g., length in bytes)
    $mysqli->set_charset($charset);
    $query = "SELECT actor_id, last_name from actor ORDER BY actor_id";
    echo "======================\n";
    echo "Character Set: $charset\n";
    echo "======================\n";
    
    if ($result = $mysqli->query($query)) {
        /* Get field information for all columns */
        $finfo = $result->fetch_fields();
        foreach ($finfo as $val) {
            printf("Name:      %s\n",   $val->name);
            printf("Table:     %s\n",   $val->table);
            printf("Max. Len:  %d\n",   $val->max_length);
            printf("Length:    %d\n",   $val->length);
            printf("charsetnr: %d\n",   $val->charsetnr);
            printf("Flags:     %d\n",   $val->flags);
            printf("Type:      %d\n\n", $val->type);
        }
        $result->free();
    }
}
$mysqli->close();
?>

Example #2 过程化风格

<?php
$link = mysqli_connect("127.0.0.1", "my_user", "my_password", "sakila");
/* check connection */
if (mysqli_connect_errno()) {
    printf("Connect failed: %s\n", mysqli_connect_error());
    exit();
}
foreach (array('latin1', 'utf8') as $charset) {
    // Set character set, to show its impact on some values (e.g., length in bytes)
    mysqli_set_charset($link, $charset);
    $query = "SELECT actor_id, last_name from actor ORDER BY actor_id";
    echo "======================\n";
    echo "Character Set: $charset\n";
    echo "======================\n";
    if ($result = mysqli_query($link, $query)) {
        /* Get field information for all columns */
        $finfo = mysqli_fetch_fields($result);
        foreach ($finfo as $val) {
            printf("Name:      %s\n",   $val->name);
            printf("Table:     %s\n",   $val->table);
            printf("Max. Len:  %d\n",   $val->max_length);
            printf("Length:    %d\n",   $val->length);
            printf("charsetnr: %d\n",   $val->charsetnr);
            printf("Flags:     %d\n",   $val->flags);
            printf("Type:      %d\n\n", $val->type);
        }
        mysqli_free_result($result);
    }
}
mysqli_close($link);
?>

以上例程会输出：

======================
Character Set: latin1
======================
Name:      actor_id
Table:     actor
Max. Len:  3
Length:    5
charsetnr: 63
Flags:     49699
Type:      2
Name:      last_name
Table:     actor
Max. Len:  12
Length:    45
charsetnr: 8
Flags:     20489
Type:      253
======================
Character Set: utf8
======================
Name:      actor_id
Table:     actor
Max. Len:  3
Length:    5
charsetnr: 63
Flags:     49699
Type:      2
Name:      last_name
Table:     actor
Max. Len:  12
Length:    135
charsetnr: 33
Flags:     20489

参见

mysqli_num_fields() Get the number of fields in a result
mysqli_fetch_field_direct() Fetch meta-data for a single field
mysqli_fetch_field() Returns the next field in the result set

The field info bit-flags used by MySql are:                                                                      
 (Thanks to ragtag at hotmail dot com)
<?php
/*
    NOT_NULL_FLAG = 1                                       
    PRI_KEY_FLAG = 2                                        
    UNIQUE_KEY_FLAG = 4                                      
    BLOB_FLAG = 16                                         
    UNSIGNED_FLAG = 32                                       
    ZEROFILL_FLAG = 64                                       
    BINARY_FLAG = 128                                       
    ENUM_FLAG = 256                                        
    AUTO_INCREMENT_FLAG = 512                                   
    TIMESTAMP_FLAG = 1024                                     
    SET_FLAG = 2048                                        
    NUM_FLAG = 32768                                        
    PART_KEY_FLAG = 16384                                     
    GROUP_FLAG = 32768                                       
    UNIQUE_FLAG = 65536
*/                                      
// To test if a flag is set you can use & like so:
 $meta = $mysqli_result_object->fetch_field();
 if ($meta->flags & 4) { 
   echo 'Unique key flag is set'; 
 } 
?>

Those wanting to map the 'type' field in this function for use in mysqli_stmt_bind_param or to cannibalize it for their own mapping may find this function useful.
function map_field_type_to_bind_type($field_type)
{
  switch ($field_type)
  {
  case MYSQLI_TYPE_DECIMAL:
  case MYSQLI_TYPE_NEWDECIMAL:
  case MYSQLI_TYPE_FLOAT:
  case MYSQLI_TYPE_DOUBLE:
    return 'd';
  case MYSQLI_TYPE_BIT:
  case MYSQLI_TYPE_TINY:
  case MYSQLI_TYPE_SHORT:
  case MYSQLI_TYPE_LONG:
  case MYSQLI_TYPE_LONGLONG:
  case MYSQLI_TYPE_INT24:
  case MYSQLI_TYPE_YEAR:
  case MYSQLI_TYPE_ENUM:
    return 'i';
  case MYSQLI_TYPE_TIMESTAMP:
  case MYSQLI_TYPE_DATE:
  case MYSQLI_TYPE_TIME:
  case MYSQLI_TYPE_DATETIME:
  case MYSQLI_TYPE_NEWDATE:
  case MYSQLI_TYPE_INTERVAL:
  case MYSQLI_TYPE_SET:
  case MYSQLI_TYPE_VAR_STRING:
  case MYSQLI_TYPE_STRING:
  case MYSQLI_TYPE_CHAR:
  case MYSQLI_TYPE_GEOMETRY:
    return 's';
  case MYSQLI_TYPE_TINY_BLOB:
  case MYSQLI_TYPE_MEDIUM_BLOB:
  case MYSQLI_TYPE_LONG_BLOB:
  case MYSQLI_TYPE_BLOB:
    return 'b';
  default:
    trigger_error("unknown type: $field_type");
    return 's';
  }
}

Here are two methods for converting the 'type' and 'flags' attributes to text for debugging purposes. They both use the predefined MYSQLI_ constants to generate the text.
<?php
public static function h_type2txt($type_id)
{
  static $types;
  if (!isset($types))
  {
    $types = array();
    $constants = get_defined_constants(true);
    foreach ($constants['mysqli'] as $c => $n) if (preg_match('/^MYSQLI_TYPE_(.*)/', $c, $m)) $types[$n] = $m[1];
  }
  return array_key_exists($type_id, $types)? $types[$type_id] : NULL;
}
public static function h_flags2txt($flags_num)
{
  static $flags;
  if (!isset($flags))
  {
    $flags = array();
    $constants = get_defined_constants(true);
    foreach ($constants['mysqli'] as $c => $n) if (preg_match('/MYSQLI_(.*)_FLAG$/', $c, $m)) if (!array_key_exists($n, $flags)) $flags[$n] = $m[1];
  }
  $result = array();
  foreach ($flags as $n => $t) if ($flags_num & $n) $result[] = $t;
  return implode(' ', $result);
}
?>

Codigos de tipos de datos devueltos por fetch_fields()
Nombre    Codigo
tinyint_  1
boolean_  1
smallint_  2
int_    3
float_    4
double_    5
real_    5
timestamp_  7
bigint_    8
serial    8
mediumint_  9
date_    10
time_    11
datetime_  12
year_    13
bit_    16
decimal_  246
text_    252
tinytext_  252
mediumtext_  252
longtext_  252
tinyblob_  252
mediumblob_  252
blob_    252
longblob_  252
varchar_  253
varbinary_  253
char_    254
binary_    254

The nax_length gives counts in bytes. So if the text is utf-8, then we get incorrect result. 
We have a code snippet where we check if the maximum length of the field and the max length of data stored becomes equal. This way we can check the potential truncation of data inserted

complete list of flags from MySQL source code:
NOT_NULL_FLAG  1    /* Field can't be NULL */
PRI_KEY_FLAG  2    /* Field is part of a primary key */
UNIQUE_KEY_FLAG 4    /* Field is part of a unique key */
MULTIPLE_KEY_FLAG 8   /* Field is part of a key */
BLOB_FLAG  16   /* Field is a blob */
UNSIGNED_FLAG  32   /* Field is unsigned */
ZEROFILL_FLAG  64   /* Field is zerofill */
BINARY_FLAG 128   /* Field is binary  */
ENUM_FLAG  256   /* field is an enum */
AUTO_INCREMENT_FLAG 512   /* field is a autoincrement field */
TIMESTAMP_FLAG 1024    /* Field is a timestamp */
SET_FLAG  2048    /* field is a set */
NO_DEFAULT_VALUE_FLAG 4096 /* Field doesn't have default value */
ON_UPDATE_NOW_FLAG 8192     /* Field is set to NOW on UPDATE */
NUM_FLAG  32768    /* Field is num (for clients) */
PART_KEY_FLAG  16384    /* Intern; Part of some key */
GROUP_FLAG 32768    /* Intern: Group field */
UNIQUE_FLAG 65536    /* Intern: Used by sql_yacc */
BINCMP_FLAG 131072   /* Intern: Used by sql_yacc */
GET_FIXED_FIELDS_FLAG (1 << 18) /* Used to get fields in item tree */
FIELD_IN_PART_FUNC_FLAG (1 << 19)/* Field part of partition func */