--------------
SELECT iden, age FROM elf WHERE sexe=1 ORDER BY iden LIMIT 3
--------------

+------+-----+
| iden | age |
+------+-----+
| M001 |  62 |
| M003 |  31 |
| M004 |  27 |
+------+-----+
3 rows in set (0.00 sec)

--------------
SELECT etud, ROUND(100*COUNT(iden)/99) FROM elf GROUP BY etud
--------------

+------+---------------------------+
| etud | ROUND(100*COUNT(iden)/99) |
+------+---------------------------+
|    0 |                         3 |
|    1 |                         6 |
|    2 |                        30 |
|    3 |                        21 |
|    4 |                        39 |
+------+---------------------------+
5 rows in set (0.00 sec)

--------------
SELECT etud, AVG(age) FROM elf GROUP BY etud
--------------

+------+----------+
| etud | AVG(age) |
+------+----------+
|    0 |  50.0000 |
|    1 |  56.8333 |
|    2 |  35.6000 |
|    3 |  35.2381 |
|    4 |  32.0000 |
+------+----------+
5 rows in set (0.00 sec)

--------------
SELECT elfetud.label, ROUND(COUNT(elf.etud)*100/99) AS eff, "%"
        FROM     elf, elfetud
        WHERE    elfetud.code=elf.etud
        GROUP BY etud
        ORDER BY eff DESC
--------------

+-------------------+------+---+
| label             | eff  | % |
+-------------------+------+---+
| supérieur         |   39 | % |
| secondaire (bepc) |   30 | % |
| baccalauréat      |   21 | % |
| primaire          |    6 | % |
| non-réponse       |    3 | % |
+-------------------+------+---+
5 rows in set (0.00 sec)

--------------
SELECT etud, AVG(age) AS moya FROM elf GROUP BY etud ORDER BY moya DESC
--------------

+------+---------+
| etud | moya    |
+------+---------+
|    1 | 56.8333 |
|    0 | 50.0000 |
|    2 | 35.6000 |
|    3 | 35.2381 |
|    4 | 32.0000 |
+------+---------+
5 rows in set (0.00 sec)

--------------
SELECT etud,
       AVG(age) AS moya
       FROM       elf
       GROUP  BY  etud
       HAVING     moya > 45
       ORDER  BY  moya       DESC
--------------

+------+---------+
| etud | moya    |
+------+---------+
|    1 | 56.8333 |
|    0 | 50.0000 |
+------+---------+
2 rows in set (0.00 sec)

--------------
SELECT etud, AVG(age) as moya
       FROM       elf
       WHERE      sexe=1
       GROUP  BY  etud
       HAVING     moya > 45
       ORDER  BY  moya       DESC
--------------

+------+---------+
| etud | moya    |
+------+---------+
|    0 | 63.0000 |
|    1 | 59.6000 |
+------+---------+
2 rows in set (0.00 sec)

--------------
select etud, AVG(age) as moya
       from       elf
       where      sexe=1
       group  by  etud
       having     moya > 45
       order  by  moya       desc
       limit 10
--------------

+------+---------+
| etud | moya    |
+------+---------+
|    0 | 63.0000 |
|    1 | 59.6000 |
+------+---------+
2 rows in set (0.00 sec)

--------------
SELECT COUNT(sexe)
        FROM tmpElf
        WHERE sexe=1
--------------

+-------------+
| COUNT(sexe) |
+-------------+
|          33 |
+-------------+
1 row in set (0.00 sec)

--------------
SELECT " SURTOUT PAS " AS incorrect , COUNT(*) FROM elf WHERE sexe=1 LIMIT 50
--------------

+---------------+----------+
| incorrect     | COUNT(*) |
+---------------+----------+
|  SURTOUT PAS  |       64 |
+---------------+----------+
1 row in set (0.00 sec)


--------------
SELECT COUNT(*) FROM (SELECT * FROM elf ORDER BY iden LIMIT 50 ) AS tmp WHERE sexe=1 ;
--------------

+----------+
| COUNT(*) |
+----------+
|       33 |
+----------+
1 row in set (0,00 sec)


Bye