Verification of dates mySQL - mysql

Question

I need to check that the steps of each project were done between the start and end dates of the project. (Write a query that allows a human to know if this is the case)
This is my code:
SELECT e.idetape,
e.idprojet,
e.datedebut,
e.datefin
FROM (SELECT idprojet,
datedebut,
datefin
FROM projet) AS p
LEFT JOIN etapexprojet AS e
ON e.datedebut < p.datedebut
AND e.datefin < p.datefin
ORDER BY idprojet;
The table of EtapexProjet (There is other date inside the table EtapexProjet ):
+---------+----------+-------------+--------------+--+
| idEtape | idProjet | dateDebut | dateFin | |
+---------+----------+-------------+--------------+--+
| 1 | 1 | 2011-07-01 | 2011-09-01 | |
| 1 | 2 | 2012-05-01 | 2012-05-10 | |
| 1 | 3 | 2011-11-01 | 2012-01-20 | |
| 2 | 1 | | | |
| 2 | 2 | | | |
| 2 | 3 | | | |
| 3 | 1 | | | |
| 3 | 2 | | | |
| 3 | 3 | | | |
| 4 | 1 | | | |
| 4 | 2 | | | |
| 5 | 2 | | | |
+---------+----------+-------------+--------------+--+
The table of Projet:
+----------+----------+-----------+------------+------------+---------------+--+
| idProjet | idClient | nomProjet | dateDebut | dateFin | idResponsable | |
+----------+----------+-----------+------------+------------+---------------+--+
| 1 | 321 | Devl. | 2011-08-01 | | 1876 | |
| 2 | 321 | Maint. | 2012-05-01 | 2012-07-23 | 2231 | |
| 3 | 345 | Devl.2 | 2011-11-01 | | 2231 | |
+----------+----------+-----------+------------+------------+---------------+--+
My expected results is that to check/verify if the beginning and ending date of each idEtape is between the beginning date and the ending date of the projet its related.

Answer 1

You don't need to use a Derived Table (sub-select query), as you are not doing any sort of aggregation, etc on the projet table.
I believe that you are only concerned with the idetape values which lie inside the projet's datedebut and datefin.
You can change Left Join to Inner Join due to above mentioned point.
I have also increased the horizon of cases to check, as there is a possibility of datefin being NULL in either of the tables.
Try the following instead:
SELECT e.idetape,
e.idprojet,
e.datedebut,
e.datefin,
p.datedebut AS projet_datedebut,
p.datefin AS projet_datefin
FROM EtapexProjet AS e
JOIN Projet AS p
ON p.idprojet = e.idprojet
AND e.datedebut >= p.datedebut
AND (e.datefin <= p.datefin OR
p.datefin IS NULL OR
e.datefin IS NULL
)
ORDER BY e.idprojet,
e.idetape;

Answer 2

Please try the code below:
SELECT nomEtape, livrable, idEtape, idProjet
FROM Etape
WHERE idEtape= (SELECT MAX(idEtape)
FROM EtapexProjet
WHERE DISTINCT(idProjet)
);