mysql_fetch_field() Function in PHP

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 availablen";
}
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 availablen";
}
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().

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