PDO creating a table with a foreign key - php

Question

I am having difficulty creating a table with MySQL (PDO) with a foreign key element, without the foreign key the table creates fine, but without I get this message:
SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax;
I have tried searching for a solution and adapting the code, but seem to keep coming across this. Is there a fix or am I being a wally?
<?php
$servername = "localhost";
$username = "root";
$password = NULL;
$dbname = "testapplciants";
try {
$conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
// set the PDO error mode to exception
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
//sql to create the activity registered table
$sql = "CREATE TABLE Activity_Register (
Activity_id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
participant_id INT(6) FOREIGN KEY (participant_id) REFERENCES participants,
entry_number INT(2),
recorded_result INT(6),
entry_date TIMESTAMP
)";
// use exec() because no results are returned
$conn->exec($sql);
echo "Table Activity Recorder created successfully";
}
catch(PDOException $e)
{
echo $sql . "<br>" . $e->getMessage();
}
$conn = null;
?>

Answer 1

PRIMARY KEY in a column's definition is shorthand for a separate definition that reads PRIMARY KEY (`column_name`)
FOREIGN KEY has no such shorthand.
`participant_id` INT(6),
FOREIGN KEY (`participant_id`) REFERENCES `participants` (`id???`)
Note that you neglected the column name for the referenced table, and you should probably also have ON DELETE and ON UPDATE parameters too.