Subqueries for php - php

Question

sorry if this might be a duplicate question but im desperatly needs help for project submission.
I have a database carpark where i have 2 table within which is carpark_availability and history.
From my code, im able to get a field "development" from table carpark_availability.
I would like to ask on how to structure my queries if i want to select * from c where my h.development = c.development.
As shown below is my code:
<?php
session_start();
$con = new mysqli('localhost','root','','carpark_project');
$dev = $_SESSION["development"];
echo "Development: ";
echo $dev;
$sql = "select * from carpark_availability where
carpark_availability.Development IN (select history.development
from history where
history.Development = '$dev' )";
//$sql = "select * from carpark_availability where development = '$dev'";
//$sql = "select * from carpark_availability where (select Development
//from history where Development= '$dev'";
$result = $con->query($sql);
while($row = $result ->fetch_assoc())
{
echo "Development: ";
echo $row["Development"]. "</br>";
echo $row["Area"]."</br>";
echo $row["weekday1"]."</br>";
}
?>

Answer 1

A join is much easier on the eye than a subquery.
SELECT c.*
FROM carpark_availability c
INNER JOIN history
USING (development)
GROUP BY development;
I'm guessing you are getting an error because your query is returning no results so $result is set to boolean false. You have nothing in your code to check for that so you are trying to call fetch_assoc() on it