php mysql删除不了中文

Question

<?php

include('houtaipost.php');
include('hosst.php');

$xxboo = $_POST['xbook'];

$tpos = new poi();
if( $tpos -> post($xxboo) ){
die('书名不能为空');
}

$xsel = "SELECT * FROM txt201807 WHERE txtname=$xxboo";
$qwe = $sql -> query( $xsel );
$sx = $qwe->fetch_array();
if ( $sx == NULL ) {
die("没有此书或书名错误");
};

$del = "DELETE FROM txt201807 WHERE txtname=$xxboo";
$sql -> query( $del );

header("location: houtai.html");

?>
前文件已加入utf8的相关代码
如果中文前面有数字，只需输入数字也能删除，例如“12书啊啊”，只需输入“12”也能删除“12书啊啊”，很奇怪