【代码笔记】php操作MySQL，实现一列数据求和

SELECT sum(求和的字段) as 输出后的字段 from 表名
SELECT sum(num) as num from cs

<?php
require_once "config.php";
$sql = "SELECT sum(num) as num from cs";
$result = mysqli_query($conn, $sql);
$row = mysqli_fetch_assoc($result);//函数从结果集中取得一行作为关联数组
echo $row['num'];//输出结果9
?>

<?php
require_once "config.php";
$sql = "SELECT sum(num) as q from cs where id = '1'";
$result = mysqli_query($conn, $sql);
$row = mysqli_fetch_assoc($result);
echo $row['q'];//输出结果3
?>