Use of MySQL explain - mysql

Question

I have this query:
EXPLAIN EXTENDED
SELECT DISTINCT
PMS_STAGIONI.DINIZVAL,
PMS_STAGIONI.DFINEVAL,
PMS_DISPO.DDATA
FROM
PMS_DISPO JOIN PMS_STAGIONI
HAVING
PMS_DISPO.DDATA BETWEEN PMS_STAGIONI.DINIZVAL AND PMS_STAGIONI.DFINEVAL
The output of explain is:
+----+-------------+--------------+-------+---------------+------------------------------+---------+------+------+----------+--------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+--------------+-------+---------------+------------------------------+---------+------+------+----------+--------------------------------+
| 1 | SIMPLE | PMS_STAGIONI | index | NULL | IDX_INIZFINEVAL_PMS_STAGIONI | 6 | NULL | 3 | 100.00 | Using index; Using temporary |
| 1 | SIMPLE | PMS_DISPO | index | NULL | IDX_DDATA_PMS_DISPO | 3 | NULL | 1199 | 100.00 | Using index; Using join buffer |
+----+-------------+--------------+-------+---------------+------------------------------+---------+------+------+----------+--------------------------------+
My question is how to calculate the product of the join using explain. For example, in this case are performed 3597 (1199x3) scans or only 1199?
1)If I add "ORDER BY DDATA" lines scanned in the table "PMS_DISPO" become 1130.
2)If I use the "WHERE" clause instead of "HAVING" clause scan no longer uses the indexes. How is it possible?
3)If i want show PMS_STAGIONI.CSTAGIONI (primary key) explain show me that:
+----+-------------+--------------+-------+---------------+---------------------+---------+------+------+----------+--------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+--------------+-------+---------------+---------------------+---------+------+------+----------+--------------------------------+
| 1 | SIMPLE | PMS_STAGIONI | ALL | NULL | NULL | NULL | NULL | 3 | 100.00 | Using temporary |
| 1 | SIMPLE | PMS_DISPO | index | NULL | IDX_DDATA_PMS_DISPO | 3 | NULL | 1130 | 100.00 | Using index; Using join buffer |
+----+-------------+--------------+-------+---------------+---------------------+---------+------+------+----------+--------------------------------+
How can I force the use of the other index?
Thanks in advance.
Edit:
The structure of "PMS_DISPO" is:
CREATE TABLE IF NOT EXISTS `PMS_DISPO` (
`ID` int(11) NOT NULL AUTO_INCREMENT ,
`CPRENOTA` int(11) NOT NULL,
`DDATA` date NOT NULL,
`CCATRIS` int(4) NOT NULL,
`NQUANT` int(4) NOT NULL,
`CAZIENDA` int(4) NOT NULL,
`CAFFILIATO` int(4) NOT NULL,
PRIMARY KEY (`ID`),
KEY `IDX_DDATA_PMS_DISPO` (`DDATA`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=1084 ;
And "PMS_STAGIONI" is:
CREATE TABLE IF NOT EXISTS `PMS_STAGIONI` (
`CSTAGIONE` int(11) NOT NULL,
`NVALIDI` tinyint(2) NOT NULL,
`BECCEZIONE` tinyint(1) NOT NULL,
`AGGSET` varchar(7) DEFAULT NULL,
`DINIZVAL` date NOT NULL,
`DFINEVAL` date NOT NULL,
`CAZIENDA` int(4) NOT NULL,
`ID` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`ID`),
KEY `CSTAGIONE` (`CSTAGIONE`),
KEY `IDX_INIZFINEVAL_PMS_STAGIONI` (`DINIZVAL`,`DFINEVAL`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=4 ;

Answer 1

A query of this sort would normally be written as follows, with indexes just as you have them...
SELECT DISTINCT s.dinizval
, s.dfineval
, d.ddata
FROM pms_dispo d
JOIN pms_stagioni s
ON d.ddata BETWEEN s.dinizval AND s.dfineval