如何从mysqli结果中检索单个列

This is my code:

<?php
$con=mysqli_connect("localhost","user","password","database");

 $post_id = '5';

$query= mysqli_query($con,"select t.tag_name from tag_map tm join article p on p.post_id = tm.post_id join tag t on t.tag_id = tm.tag_id where p.post_id = '$post_id'");
while($que = mysqli_fetch_row($query))
{
echo "<pre>";
print_r($que);
} 
?>

This is output I got:

Array
(
    [0] => audit
)
Array
(
    [0] => income tax
)

The output is not exactly what I want. I need exactly only the values like audit, income tax only. Can any one help me?

Needed Output :

audit

income tax

For starters, you should be using prepared statements to avoid SQL injection. After that, you can use either mysqli::bind_result OR mysqli_stmt::get_result and mysqli_result::fetch_array. I'll demonstrate both methods here.

It is important to take these practices on board, you are using mysqli instead of mysql, so it makes sense to avail yourself of the enhanced features this library brings to bear.

First, preparing a statement:

// initiate database connection
$db = mysqli_connect(
    "localhost",
     "user",
     "password",
     "database"
);

// set up your statement with ? parameters
$statment = $db->prepare('
    SELECT 
        t.tag_name 
    FROM 
        tag_map tm 
    JOIN 
        article p ON
            p.post_id = tm.post_id 
    JOIN 
        tag t ON 
            t.tag_id = tm.tag_id 
    WHERE
        p.post_id = ?
');

// bind values for each parameter
$statement->bind_param('i', $post_id);

// execute the statement
$statement->execute();

The code above will safely prepare the query and fire it at the database, you've got some results to work with now. As mentioned, you can use two different methods. First is bind_result, as follows:

// list the columns you want to get from each row as variables
$statement->bind_result($tagName);

// then loop the results and output the columns you bound above
while($statement->fetch()){
    echo $tagName.'<br>';
}

The second method is to use get_result, then loop those results and use fetch_array to grab an associative array, from which you can get the column you're after, as follows:

$result = $statement->get_result();
while ($row = $result->fetch_array(MYSQLI_ASSOC)) {
    echo $row['tag_name'].'<br>';
}

... in either case, use free_result when you're done.

$statement->free_result();

Documentation

• mysqli::prepare - http://www.php.net/manual/en/mysqli.prepare.php
• mysqli_stmt::get_result - http://www.php.net/manual/en/mysqli-stmt.get-result.php
• mysqli_stmt::bind_param - http://www.php.net/manual/en/mysqli-stmt.bind-param.php
• mysqli_stmt::bind_execute - http://www.php.net/manual/en/mysqli-stmt.execute.php
• mysqli_stmt::bind_result - http://www.php.net/manual/en/mysqli-stmt.bind-result.php
• mysqli_stmt::fetch - http://www.php.net/manual/en/mysqli-stmt.fetch.php
• mysqli_result::fetch_array - http://www.php.net/manual/en/mysqli-result.fetch-array.php

<?php
$con=mysqli_connect("localhost","user","password","database");

 $post_id = '5';

$query= mysqli_query($con,"select t.tag_name from tag_map tm join article p on p.post_id = tm.post_id join tag t on t.tag_id = tm.tag_id where p.post_id = '$post_id'");
while($que = mysqli_fetch_row($query))
{
   echo $que[0];
} 
?>

Try with $que[0]:

while($que = mysqli_fetch_row($query))
{
echo "<pre>";
print_r($que[0]);
} 

Try this,

<?php

while($que = mysqli_fetch_row($query))
{
    echo "<pre>";
    echo $que[0];
} 
?>

If you just want to get the result as an assoc array and don't want to use bind_param etc. you could just use php function array_column with the specific column name on your result:

$result = array_column($connection->query('SELECT xy FROM table')->fetch_all(MYSQLI_ASSOC), 'xy');