The best way to run completely unrelated queries together? - php

Question

I seem to be running into this issue often, usually for checking to see if a $_GET['id'] actually exists in my database before running another query, related or not to the id being received.
If a record exists with the same id, then I show the HTML, e.g.:
if ($r) { #query was successful
$num = mysqli_num_rows($r);
if ($num == 1) {
?>
<form method="post">
...
<input type="submit" value="Submit" />
</form>
<?php
} else {
echo 'No records';
}
} else {
echo 'Query Failed';
}
mysqli_free_result($r);
The above works, but let's say that I want to perform another unrelated query between my opening/closing form tags; would it be proper to simply do something like this, which I would consider a nested query:
$q = "SELECT id FROM stuff WHERE id = $id";
$r = #mysqli_query($dbc, $q);
if ($r) { #query was successful
$num = mysqli_num_rows($r);
if ($num == 1) {
?>
<form method="post">
<?php
$q = "SELECT example FROM somewhere";
$r = #mysqli_query($dbc, $q);
if ($r) {
$num = mysqli_num_rows($r);
if ($num > 0) {
while ($row = mysqli_fetch_array($r, MYSQLI_ASSOC)) {
echo $row['example'];
}
}
} else {
echo 'Query failed';
}
?>
<input type="submit" value="Submit" />
</form>
<?php
} else {
echo 'No records';
}
} else {
echo 'Query Failed';
}
mysqli_free_result($r);
Or maybe create a boolean, like so:
$id_status = 0;
$q = "SELECT id FROM stuff WHERE id = $id";
$r = #mysqli_query($dbc, $q);
if ($r) { #query was successful
$num = mysqli_num_rows($r);
if ($num == 1) {
$id_status = 1;
}
}
mysqli_free_result($r);
if ($id_status) { #Run another query
...
}
I currently have a problem when it comes to requiring two separate query results for one task: (1) generating inputs from another table, (2) displaying the current values, (3) checking to see what input that has been generated matches the current value, e.g.:
$q = "SELECT id, food FROM restaurants";
$q = "SELECT favFood FROM people WHERE id = 1"; #favFood is equal to the id of food
...
while ($row = mysqli_fetch_array($r, MYSQLI_ASSOC)) {
?>
#generate all food from table, make favFood the current selected input
<input type="radio" name="yum" value="<?php echo $row['id']; ?>" />
<?php
}
So as you can see, I am having trouble when it comes to unrelated queries; the last example would probably work with a UNION or something, but i'd have a bunch of repeated rows displaying favFood, so it doesn't feel right, e.g.:
favFood | id | food
1 | 1 | Pizza
1 | 2 | Burgers
1 | 3 | Monkey Brains
Before I end this, I just want to say that I have made an attempt to use mysqli_multi_query, but I most likely did something wrong; i'm not even sure if it would work in this case, or what it does exactly.
Thanks!

Answer 1

If you want to check whether a record exists multiple times in your code, I suggest to create a function which returns a bool.
function record_exists($dbc, $q){
$state = false;
if($r = #mysqli_query($dbc, $q)){
if(mysqli_num_rows($r) == 1){
$state = true;
}
mysqli_free_result($r);
}
return $state;
}
$q = "SELECT id FROM stuff WHERE id = $id";
if(record_exists($dbc, $q)){
echo 'Yay, it exists';
}
Then if you want to SELECT some fields from a table but the filter depends on a value from another table, you could JOIN two tables in the query like so:
SELECT restaurants.id, restaurants.food
FROM restaurants
JOIN people ON restaurants.id = people.favFood
WHERE people.id = 1
Now you only SELECT the fields you want from table restaurants and filter them on a person id from the table people.

Answer 2

Two reasons why you've got such a problem
You are doing A LOT of useless stuff.
no one needs you "query failed" statement.
num rows check is also superfluous
most of the code you write is just repetitions
Like PHP users from the last century you are mixing database calls with HTML output. Now you see that the term "spaghetti code" was coined for a reason.
Your database related code rewritten with simple mysqli wrapper:
$rows = [];
$found = $db->getOne("SELECT id FROM stuff WHERE id = ?i", $id);
if ($found) {
$rows = $db->getAll("SELECT example FROM somewhere");
}
Now you can proceed to HTML output, either inline or (better) by including a template
?>
<?php if ($rows): ?>
<form method="post">
<?php foreach ($rows as $row): ?>
<?=$row['example']?>
<?php endforeach ?>
<input type="submit" value="Submit" />
</form>
<?php else: ?>
No records
<?php endif ?>