PHP Mysql Tutorials, Function, mysql_fetch

Topic

What is mysql_fetch_field() function in PHP?
How does mysql_fetch_field() works?

Explanation

This mysql_fetch_field() function gets column information from a query result and returns as an object.

Syntax

object mysql_fetch_field ( resource result [, int field_offset])

Returns an object, using that we can get required information about the field.

The properties of the object are:

name - column name
table - name of the table the column belongs to
def - default value of the column
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

mysql_fetch_field() retrieves the column information for a field in a query. If you specify an offset to mysql_fetch_field(), the column properties for that field are returned. If you don't specify an offset, the data for the next field in order will be returned.

Example:

<?php

//Attempt to connect to the default database server

$link = mysql_connect("mysql_host", "mysql_user", "mysql_password")
or die ("Could not connect");

//select database

if (!mysql_select_db("my_database", $link)) {
echo " ERROR NO: " . mysql_errno($link) . "\n";
}

// Simple Select query

$query = "SELECT * FROM my_table";
$res=mysql_query($query,$link);

/* get column metadata */

echo "Information for column 0:\n";
$meta = mysql_fetch_field($res,0);
if (!$meta) {
echo "No information available\n";
}

echo"

    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";

mysql_free_result($res);

?>

The output of above code is given below for one filed only, but same way for other fields also we can get the result.

Result:

Information for column 0:
blob: 0
max_length: 2
multiple_key: 0
name: id
not_null: 1
numeric: 1
primary_key: 1
table: type
type: int
unique_key: 0
unsigned: 0
zerofill: 0

The same code can be altered to dispaly field information of all the fields in the result set returned by mysql_query() function.

<?php

/* get column metadata */

$i = 0;
while ($i < mysql_num_fields($res)) {
echo "Information for column $i:\n";
$meta = mysql_fetch_field($res);
if (!$meta) {
echo "No information available\n";
}

echo"

    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";

$i++;
}

mysql_free_result($res);

?>

Replace the above code in the previous example to display field information of all the fields.

See also: mysql_field_seek().

mysql_fetch_field() Function in PHP