如何从数据库中的三个表中同时获取数据

Question

i want to fetch the data from three tables from my database all together and show them on a webpage. there have found many similar questions like this but none of them helped me. here my php code is

<?php

session_start();
include('database.php');

$sql = "SELECT * FROM class8,class9,class10 WHERE teacher_id = :id";
$stmt = $conn->prepare($sql);
$stmt->bindParam(':id', $_SESSION['teacher_id']);

$result = $stmt->execute();
while ($row = $stmt->fetch(PDO::FETCH_OBJ)) {

    var_dump($row);
}

?>

from this code i have tried to fetch but it gives error like this

Fatal error: Uncaught PDOException: SQLSTATE[23000]: Integrity constraint violation: 1052 Column 'teacher_id' in where clause is ambiguous in C:\xampp\htdocs\kridha\prospectcorse.php:10 Stack trace: #0 C:\xampp\htdocs\kridha\prospectcorse.php(10): PDOStatement->execute() #1 {main} thrown in C:\xampp\htdocs\kridha\prospectcorse.php on line 10

how to do that..??/

Answer 1

you need to join the tables, and specify the table names when referring to columns that exist in multiple tables.

SELECT *
FROM class8
JOIN class9 ON class8.teacher_id = class9.teacher_id
JOIN class10 ON class8.teacher_id = class10.teacher_id
WHERE class8.teacher_id = :id