合併兩個準備好的語句不起作用

Question

首先，根據另一個SO post，我嘗試將這兩個語句合併爲一個。

<?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，這一直拋出錯誤：Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error on line 71。

我找不到任何相關的解決方案來解決這個問題，所以我決定簡單地分開兩個陳述。

<?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var_dump($result)正在恢復Bool(false)，所以很明顯的東西不與獲取的結果，把它作爲一個變量權工作，現在看來，在這兩種情況下。

我是新來的PHP和MySQL，所以我現在虧本了。

Answer 1

改變這一狀況，

$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"]; 

對此，

$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"]; 

你缺少查詢的執行。