Execute an SQL query inside another SQL query - php

Question

Ok, I assume that the title is not the best title, but let me explain my problem: I'm creating a website that needs to show posts of people (anyway), and I have to show their gravatar's profile picture, so this what I did:
<?php
function get_gravatar( $email, $s = 80, $d = 'mm', $r = 'g', $img = false, $atts = array() ) {
$url = 'https://www.gravatar.com/avatar/';
$url .= md5( strtolower( trim( $email ) ) );
$url .= "?s=$s&d=$d&r=$r";
if ( $img ) {
$url = '<img src="' . $url . '"';
foreach ( $atts as $key => $val )
$url .= ' ' . $key . '="' . $val . '"';
$url .= ' />';
}
return $url;
}
require("db.php");
$sql = "SELECT * FROM posts ORDER BY date DESC";
foreach ($db->query($sql) as $row) {
// var_dump($row);
$user = $row['user_id'];
$sql_user = "SELECT email FROM users WHERE id = $user";
foreach ($db->$sql_user as $row_user) {
var_dump($row_user);
echo "<img src=\"".get_gravatar($row_user['email'])."\"/>";
}
echo "<h2>".$row['title']."</h2><br/>";
echo "<p>".$row['content']."</p><br/>";
}
But, it doesn't work (well, it works, but it doesn't shows me the profile picture of the user, only the post).
So, I think the problem is that I can't call 2 times the variable $db at the same time, but I'm not sure, so that's m=why I'm asking if there is a way to fix my problem or to select 2 tables at the same time.

Answer 1

you can short your logic
$sql="SELECT u.email "
. "FROM posts AS p "
. "LEFT JOIN users AS u "
. "ON u.id=p.user_id "
. "ORDER BY p.date DESC";

Answer 2

use join
SELECT * FROM users join posts on users.id =Posts.user_id ORDER BY date DESC

Answer 3

you don't apply query to sql string in second foreach
foreach ($db->query($sql_user) as $row_user) {

Answer 4

see your second foreach you miss to put query function
foreach ($db->query($sql) as $row) {
foreach ($db->query($sql_user) as $row_user) {

Answer 5

You could just use JOIN
JOIN clause is used to combine rows from two or more tables, based on
a related column between them.