Combining two prepared statements not working - php

Question

First, according to another SO post, I tried combining the two statements into one.
<?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
?>
However, this kept throwing the error: Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error on line 71.
I couldn't find any relevant solutions to this issue, so I decided to simply split up the two statements.
<?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"] = $result["prim"];
?>
But a var_dump($result) is returning Bool(false), so obviously something is not working right with fetching the result and storing it as a variable, it seems, in both cases.
I'm new to PHP and MySQL, so I'm at a loss right now.

Answer 1

Change this,
$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"];
To this,
$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"];
You are missing the execution of the query.