php删除sql查询不工作

在重用$sql变量之前，需要执行query1

<?php
    include('session.php');
?>

<?php
    $conn = new mysqli("127.0.0.1","root","","foo");
    if ($conn->connect_errno) {
        echo "Failed to connect to MySQL: (" . $conn->connect_errno . ") " .         $conn->connect_error;
    }
    $sew = $_SESSION['login_user'];
    $a = $_GET["en"];
    $l = 1;
    $d = -1;

    if($a == 1)
    {
        $sqlw = " INSERT into dlkeuser VALUES('$a','$sew')" ;

        if ($conn->query($sqlw) === FALSE) 
        {
            echo "you have already disliked the song";
        }
        else
        {
        //query1
            $sql = " DELETE FROM lkeuser WHERE userid = '$sew' AND songid = '$a' ";

        //query2
            $sql = "UPDATE liking
            SET count = count - 1 ";

            if ($conn->query($sql) === TRUE) {
                echo "you disliked the song";
            } 
            else {
                echo "Error: " . $sql . "<br>" . $conn->error;
            }
        }

---

您没有在任何地方执行查询1。下面的代码不会执行您的查询

 //query1
   $sql  = " DELETE FROM lkeuser WHERE userid = '$sew' AND songid = '$a' " ;
   $conn->query($sql);

 //query2
       $sql = "UPDATE liking
       SET count = count - 1 ";

       if ($conn->query($sql) === TRUE) {

您需要另一行，如下所示（就像您在query2中所做的那样）

if（$conn->query（$sql）==TRUE）{
回声“你喜欢这首歌”；
} 
否则{
echo“Error:”.$sql.“
”$conn->Error；
}

这将执行查询并检查错误。

让我们试试这个

它会起作用的

if ($conn->query($sql) === TRUE) {

    echo "you liked the song";
} 
else {
      echo "Error: " . $sql . "<br>" . $conn->error;
}

表示了解的语句。即使是这样也不安全！您的代码对SQL注入非常开放，因此您目前甚至无法控制您执行的SQL代码。在运行时，实际的SQL代码是什么
echo
要查找的
$sql
变量。这是你期望的代码吗？当您在数据库上手动执行该代码时，会发生什么情况？您需要单独执行查询。在执行删除之前，您将覆盖
$sql
。通过在执行之前将$sql设置为其他字符串，将删除查询替换为插入查询。还有，记住@Jay Blanchard说的话。
if ($conn->query($sql) === TRUE) {

    echo "you liked the song";
} 
else {
      echo "Error: " . $sql . "<br>" . $conn->error;
}

<?php
    include('session.php');
?>

<?php
    $conn = new mysqli("127.0.0.1","root","","foo");
    if ($conn->connect_errno) {
       echo "Failed to connect to MySQL: (" . $conn->connect_errno . ") " .           $conn->connect_error;
    }
    $sew = $_SESSION['login_user'];
    $a = $_GET["en"];
    $l = 1;
    $d = -1;

    if($a == 1)
    {
    $sqlw = " INSERT into dlkeuser VALUES('$a','$sew')";

        if ($conn->query($sqlw) === FALSE) 
        {
            echo "you have already disliked the song";
        }
        else
        {
        //query1
            $sql  = " DELETE FROM lkeuser WHERE userid = '$sew' AND songid = '$a' " ;

        //query2
            $sql1 = "UPDATE liking
            SET count = count - 1 ";

            if ($conn->query($sql) === TRUE) {
                echo "deleted the song";
            }

            if ($conn->query($sql1) === TRUE) {
                echo "you disliked the song";
            } 
            else {
                echo "Error: " . $sql . "<br>" . $conn->error;
            }
        }