Put a PHP variable in a SQL Query - php

Question

I have the following code:
try
{
$sql = 'SELECT id, type, date, amount, description, category
FROM `transactions`
WHERE type = "income"
AND month(date) = '$monthselect'
ORDER BY `transactions`.`id` DESC
LIMIT 0,50';
$result2 = $pdo->query($sql);
}
Now, I want to give this month(Date) a variable which month I want to select. if I put 1, it will give me January. So i thought, if I define a variable with 1, I can use it to select a month, right?
$monthselect = 1;
It doesnt work. What am I doing wrong?

Answer 1

Use prepared statements:
$stm = $pdo->prepare('SELECT id, type, date, amount, description, category
FROM `transactions`
WHERE type = "income"
AND month(date) = ?
ORDER BY `transactions`.`id` DESC
LIMIT 0,50');
$stm->execute(compact('monthselect'));
$result2 = $stm->fetchAll();
Since you're not adding "1" directly in your query, I'm assuming here that the variable comes from user input.

Answer 2

To concatenate strings in PHP you need to use the . operator.
$sql = 'SELECT id, type, date, amount, description, category
FROM `transactions`
WHERE type = "income"
AND month(date) = ' . $monthselect . '
ORDER BY `transactions`.`id` DESC
LIMIT 0,50';

Answer 3

I'll frequently use double quotes to substitute variables in PHP:
$sql = "SELECT id, type, date, amount, description, category
FROM `transactions`
WHERE type = 'income'
AND month(date) = $monthselect
ORDER BY `transactions`.`id` DESC
LIMIT 0,50";
Note that you need to swap the existing double quotes (inside the string) to single quotes. You can escape them too, but I find this way makes it much more readable.

Answer 4

Your issue is that you are trying to use a variable inside single quotes, inside which php is not translated
I find by using double quote marks around my queries it allows me to not only use variables in them but to also be able to use single quote mark around the values passed to the db
$sql = "SELECT id, type, date, amount, description, category
FROM `transactions`
WHERE type = 'income'
AND month(date) = $monthselect
ORDER BY `transactions`.`id` DESC
LIMIT 0,50";