Question

This question is more on this post. So I want to retrieve the number in a certain column. So let’s say the table looks like this:

A | B | C | D | E | F
---------------------
0 | 50| 0 | 0 | 0 | 0

Let’s say the user enters in B, I want to go fetch the current number in the table, which is 50. This is my SQL code:

$link = new PDO('**;dbname=**;charset=UTF-8','**','**');
$stmt = $link->prepare("SELECT MAX(:type) as max FROM table");
$stmt->bindParam(':type', $type);
$stmt->execute();
$used = $stmt->fetch(PDO::FETCH_ASSOC);
$used = $used["max"];

But this is just returning B rather than the number. How do I change my code to get the number? Thanks

Answer 1

SELECT MAX(:type) as max FROM table

Assuming :type gets set to “B”, this will be executed as:

SELECT MAX("B") as max FROM table

The MAX of something with just one value will be that one value, i.e.:

SELECT "B" as max FROM table

Most likely you want to select the MAX from that column, not the string:

SELECT MAX(B) as max FROM table

Which you can do like this:

$stmt = $link->prepare("SELECT MAX($type) as max FROM table");

Obviously, this is vulnerable to SQL injection if $type comes from a user, but if you’re getting a table name from a user, then you’re doing something wrong anyway.

It’s also possible that your table would make more sense like this:

type | value
------------
A    | 0
B    | 50
C    | 0

And then you could get it with:

SELECT MAX(value) FROM tableName WHERE type = :type