checking room availability for hotel booking system : hello i'm trying to check available rooms in booking system so i have two tables : table of rooms called chambre (`id`,`name`) and table reservation_client(`id`,`start`,`end`,`id_chambre`) the start and end are the check in and checkout dates. 

my query is :  

```
 $sql = "SELECT * FROM chambre WHERE id NOT IN (SELECT id_chambre FROM reservation_client WHERE end < '2019-07-20'  AND start > '2019-07-19 ')";
```

but its not give me any result .