PHP - 2 Insert Queries

Good day everyone. I go by the nickname Sbosh and I am a newbie in PHP.

I am currently learning php using video tutorials. I need help with regards to php queries.

I have the following code:

"SELECT 'food', 'calories' FROM 'diet' ORDER BY 'id'"

which is supposed to display content from a table inside phpmyadmin which i created manually using phpmyadmin. But It gives an error saying i must check the MariaDB version on how to right this query, something like that.

Please assist on the proper way of writing this code. Again I am a newbie in PHP and just starting to learn, so your help will be highly appreciated.

$query1 = "SELECT * FROM forums WHERE MATCH (topics) AGAINST ('$keywords' IN BOOLEAN MODE)";

$query2 = "SELECT * FROM users WHERE username='$username";

function getContent() {
	include 'connection.php';

$dx = date('m', strtotime('today - 30 days'));	

	if (!isset($_POST["month_select"])) {
		$month = $dx;
		$year = "2014";
	}
	else {
		$month = $_POST["month_select"];
		$year = $_POST["year_select"];
	}

//last fuel fill value 
		$query2 = "SELECT d.liter as FirstFill 
  FROM members AS m
LEFT OUTER
  JOIN diesel AS d
    ON d.userid = m.id
   WHERE YEAR(dato) = $year AND MONTH(dato) = $month AND d.liter > 0 ORDER BY d.id ASC LIMIT 1";

		$sql2=$oDB->prepare($query2);
		$sql2->execute();
		$row2 = $sql2->fetchAll();
    return $row2;
	
    $FirstFill = $row2['FirstFill'];
	
		$query = "SELECT m.username, m.id, 10 * (SUM(d.liter) - $FirstFill) / (MAX(d.km) - MIN(d.km)) as AvgFuel 
  FROM members AS m
LEFT OUTER
  JOIN diesel AS d
    ON d.userid = m.id
   WHERE YEAR(dato) = $year AND MONTH(dato) = $month AND d.liter > 0
GROUP
    BY m.id ORDER BY AvgFuel ASC";
	
		$sql=$oDB->prepare($query);
		$sql->execute();
		$row = $sql->fetchAll();
    return $row;

	}

<?php
function childtheme_cat_limited_blog( $query ) {
    if ( $query->is_home() && $query->is_main_query() ) {
        $query->set( 'events_categories', 'mycategory1' );
    }
}
add_action( 'pre_get_posts', 'childtheme_cat_limited_blog' );
?>

<?php
function childtheme_cat_limited_blog( $query ) {
    if ( $query->is_home() && $query->is_main_query() ) {
        $query->set( 'category_name', 'mycategory2' );
    }
}
add_action( 'pre_get_posts', 'childtheme_cat_limited_blog' );
?>

/* No filtering and no unread */
$q_urls = "SELECT * FROM shortenified_urls WHERE is_social = '1' AND active = '1' ORDER BY date_added DESC";

/* All links in a particular category */
$q_urls = "
SELECT * FROM shortenified_urls
WHERE shortenified_urls.primary_cat = $vu_cat_view
OR EXISTS (
SELECT link_id FROM linkcats
WHERE link_id = shortenified_urls.id AND cat_id = $vu_cat_view
)
AND shortenified_urls.is_social = '1' AND shortenified_urls.active = '1'
ORDER BY date_added DESC"
;

/* Unread only for all categories */
$q_urls = "SELECT * FROM shortenified_urls
WHERE shortenified_urls.date_added > $vu_mark_as_read
AND NOT EXISTS (
SELECT lid FROM linkviews
WHERE lid = shortenified_urls.id AND uid = $viewing_user_id
)
AND shortenified_urls.is_social = '1' AND shortenified_urls.active = '1'
ORDER BY date_added DESC"
;

/* Unread links in a particular category */
$q_urls = "
SELECT * FROM shortenified_urls
WHERE shortenified_urls.primary_cat = $vu_cat_view AND shortenified_urls.date_added > $vu_mark_as_read
OR EXISTS (
SELECT link_id FROM linkcats
WHERE link_id = shortenified_urls.id AND cat_id = $vu_cat_view
)
AND NOT EXISTS (
SELECT lid FROM linkviews
WHERE lid = shortenified_urls.id AND uid = $viewing_user_id
)
AND shortenified_urls.is_social = '1' AND shortenified_urls.active = '1'
ORDER BY date_added DESC"
;