结合两个准备好的语句不起作用

Question

首先，根据另一个SO post，我尝试将这两个语句合二为一。

<?php
  $conn->setAttribute(PDO::ATTR_EMULATE_PREPARES, 1);
  $sql  = "UPDATE users SET pass = :password WHERE usrn = :id;
           SELECT prim FROM users WHERE usrn = :id;";
  $stmt = $conn->prepare($sql);
  $stmt->bindParam(":id", $_SESSION["idPersist"]);
  $stmt->bindParam(":password", password_hash($_POST["password"], PASSWORD_DEFAULT));
  $stmt->execute();
  $result = $stmt->fetch(PDO::FETCH_ASSOC); //// line 71
?>

但是，这一直抛出错误：Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error on line 71。

我找不到任何相关的解决方案来解决这个问题，所以我决定简单地将这两个语句分开。

<?php
  $sql  = "UPDATE users SET pass = :password WHERE usrn = :id";
  $stmt = $conn->prepare($sql);
  $stmt->bindParam(":id", $_SESSION["idPersist"]);
  $stmt->bindParam(":password", password_hash($_POST["password"], PASSWORD_DEFAULT));
  $stmt->execute();
  $sql  = "SELECT prim FROM users WHERE usrn = :id";
  $stmt = $conn->prepare($sql);
  $stmt->bindParam(":id", $_SESSION["idPersist"]);
  $stmt->execute();
  $result = $stmt->fetch(PDO::FETCH_ASSOC);
  $_SESSION["session"] = $result["prim"];
?>

但是var_dump($result) 正在返回Bool(false)，因此显然在这两种情况下都无法正常获取结果并将其存储为变量。

我是 PHP 和 MySQL 的新手，所以我现在很茫然。

Answer 1

改变这个，

$sql  = "SELECT prim FROM users WHERE usrn = :id";
$stmt = $conn->prepare($sql);
$stmt->bindParam(":id", $_SESSION["idPersist"]);
$result = $stmt->fetch(PDO::FETCH_ASSOC);
$_SESSION["session"] = $result["prim"];

对此，

$sql  = "SELECT prim FROM users WHERE usrn = :id";
$stmt = $conn->prepare($sql);
$stmt->bindParam(":id", $_SESSION["idPersist"]);
$stmt->execute(); // Your problem
$result = $stmt->fetch(PDO::FETCH_ASSOC);
$_SESSION["session"] = $result["prim"];

您错过了查询的执行。