Question: I have 2 db tables - one is including all the entries, the other one is the "blacklist" - means i want to select all values excluding the entries of table 2

```
$req = "SELECT * FROM table1 WHERE link_id != (SELECT id FROM table2)";
$stmt = $pdo->query($req);

foreach($stmt as $data) {

echo $data['link_id']."<br>";           

}

```

Can anyone help me out?

Answer: 
Just use an `int` instead. Otherwise, make your own boolean type:

```
enum { false, true };
typedef int bool;

```

If you want to store many booleans, consider

```
typedef char bool;

```

instead. Notice that neither make a “real” boolean type, as it can assume other values than just 0 and 1. Use the C convention that 0 indicates falsehood while every other value indicates truth.
C99 has the `<stdbool.h>` header.