更新-在提出一些建议后，我将其改为使用$wpdb API。以下代码正在重新调整“1”，而不是实际结果计数，实际结果计数应为“2”。

//a function is a block of code we can call everything between { } is the functions code. The return is the output.
function reservations_yesterday() {
global $wpdb;

              //query DB… get_var should get the output from the db and store it in the results variable. 
$results = $wpdb->get_var ("SELECT SUM(`mattiscool`), booking_date FROM `wp_cbxrbooking_log_manager` WHERE `booking_date` = CURDATE() -1");

//return the results, sends the output back to the code that calls the function.
return $results;
}


// this is a function, and you that calls the reservations_yesterday functions, and you are assigning the shortcode tag of res-1
add_shortcode(\'res-1\', \'reservations_yesterday\');

原创-有人能带领一个人学习如何在这条船上钓鱼吗？我有一个customshort代码文件。我知道第一个代码的文件及其挂钩是正确的，因为它可以正常工作。我正在尝试添加一个带有SUM的SQL查询的短代码。我知道sql字符串是好的，因为它已经过验证。我在degudding上遇到了一些我没有遇到的错误。以前，我在插件中使用相同的php代码，但现在改为使用短代码，而不使用插件。

代码：

// how many reservations yesterday
function res_yesterday(){

$servername = "localhost";
$username = "site";
$password = "pass";
$dbname = "site";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
  die("Connection failed: " . $conn->connect_error);
}

$sql = "SELECT SUM(`mattiscool`) ,booking_date as \\\'total\\\' FROM `wp_cbxrbooking_log_manager` WHERE `booking_date` = CURDATE() -1";

$result = mysqli_query($sql);

while ($row = mysqli_fetch_assoc($result))
{ 
   echo $row[\'total\'];
}

mysqli_close($con);


}
add_shortcode(\'res_1\', \'res_yesterday\');

错误：

警告：mysqli\\u query（）需要至少2个参数，1个在/home/food/domains/xxx中给定。com/public\\u html/wp-content/themes/yummy/custom-shortcode。php第29行

警告：mysqli\\u fetch\\u assoc（）要求参数1为mysqli\\u result，在/home/food/domains/xxx中为空。com/public\\u html/wp-content/themes/yummy/custom-shortcode。php第31行

警告：mysqli\\u close（）要求参数1为mysqli，在/home/food/domains/xxx中为null。com/public\\u html/wp-content/themes/yummy/custom-shortcode。php第36行

有人能告诉我我做错了什么吗？

function reservations_yesterday() {
global $wpdb;


$results = $wpdb->get_var ("SELECT SUM(`mattiscool`), booking_date FROM `wp_cbxrbooking_log_manager` WHERE `booking_date` = CURDATE() -1");

return $results;
}



add_shortcode(\'name\', \'reservations_yesterday\');