Use SET #variable=? inside of mysqli prepared statement - php

Question

i have a query that uses a few variables in mysql. The query looks something like this:
SET #var1 = 1;
SET #var2 = 2;
SELECT * FROM table WHERE table.column1=#var1
AND table.column2=#var2
AND table.colum3=#var1 * #var2;
I would like to make a prepared statement like:
$sql=' SET #var1 = ?;
SET #var2 = ?;
SELECT * FROM table WHERE table.column1=#var1
AND table.column2=#var2
AND table.colum3=#var1 * #var2;'
and then just bind two params to it. But this gives me an mysql sytax error near the SET #var1=?;
Of course, in the example, I could bind three variables and do the calculations before querying. In my real query there are more advanced calculations and I would need to bind the same variable to multiple places. And that seems like repeating and bad coding practice.
Any solutions for this?

Answer 1

PHP offers prepared statements and parametrized queries out of the box, you can just use them.
$var1 = 1;
$var2 = 2;
$connection = new PDO($dsn, $user, $password);
$sql = 'SELECT * FROM table WHERE table.column1=:var1 AND table.column2=:var2 AND table.colum3=:varSum';
$statement = $connection->prepare($sql);
$statement->bindValue(':var1', $var1, PDO::PARAM_INT);
$statement->bindValue(':var2', $var2, PDO::PARAM_INT);
$statement->bindValue(':varSum', $var1 + $var2, PDO::PARAM_INT);
$statement->execute();
This code is just an example, it is not tested.

Answer 2

you should use multi_query
<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";
// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
$sql=' SET #var1 = '.$v1.';
SET #var2 = '.$v2.';
SELECT * FROM table WHERE table.column1=#var1
AND table.column2=#var2
AND table.colum3=#var1 * #var2;'
if ($conn->multi_query($sql) === TRUE) {
echo "New records created successfully";
} else {
echo "Error: " . $sql . "<br>" . $conn->error;
}
$conn->close();
?>

Answer 3

Here's an alternative solution: feed your values in to a subquery, then you can reference them from there:
function GetStuffFromTable(mysqli $db, int $column1, int $column2): array
{
$sql = '
SELECT *
FROM (SELECT ? var1, ? var2) vars
INNER JOIN table
ON table.column1 = vars.var1
AND table.column2 = vars.var2
AND table.column3 = vars.var1 * vars.var2;
';
$statement = $db->prepare($sql);
try
{
$statement->bind_param("ii", $column1, $column2);
$statement->execute();
$result = $stmt->get_result();
return $statement->fetch_all($result);
} finally {
$statement->close();
}
}
Note: I came here looking for an answer to the same question / I don't know PHP well, so can't comment on the quality of this solution from a PHP perspective.