'WHERE' is the same of 'on' in mysql(many times,but not always)

set profiling = 1;

show profiles;

select ia.applicationid, ia.itemid, i.name, i.hostid, i.key_, hl.value from items_applications ia
inner join applications a on ia.applicationid = a.applicationid and ia.applicationid = 242
inner join items i on ia.itemid = i.itemid and (i.key_ like 'log%' or i.key_ like 'logrt%')
inner join history_log hl on i.itemid = hl.itemid
order by ia.applicationid, ia.itemid, i.key_


select ia.applicationid, ia.itemid, i.name, i.hostid, i.key_, hl.value from items_applications ia
inner join applications a on ia.applicationid = a.applicationid and ia.applicationid = 242
inner join items i on ia.itemid = i.itemid
inner join history_log hl on i.itemid = hl.itemid
where i.key_ like 'log%' or i.key_ like 'logrt%'
order by ia.applicationid, ia.itemid, i.key_

show profiles;

+----------+----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Query_ID | Duration | Query                                                                                                                                                                                                                                                                                                  |
+----------+----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
|        1 | 0.034328 | select ia.applicationid, ia.itemid, i.name, i.hostid, i.key_, hl.value from items_applications ia
inner join applications a on ia.applicationid = a.applicationid and ia.applicationid = 242
inner join items i on ia.itemid = i.itemid and (i.key_ like 'log%' or i.key_ like 'logrt%')
inner join histo |
|        2 | 0.019305 | select ia.applicationid, ia.itemid, i.name, i.hostid, i.key_, hl.value from items_applications ia
inner join applications a on ia.applicationid = a.applicationid and ia.applicationid = 242
inner join items i on ia.itemid = i.itemid
inner join history_log hl on i.itemid = hl.itemid
where i.key_ l   |
|        3 | 0.023647 | select ia.applicationid, ia.itemid, i.name, i.hostid, i.key_, hl.value from items_applications ia
inner join applications a on ia.applicationid = a.applicationid and ia.applicationid = 242
inner join items i on ia.itemid = i.itemid and (i.key_ like 'log%' or i.key_ like 'logrt%')
inner join histo |
|        4 | 0.335506 | select ia.applicationid, ia.itemid, i.name, i.hostid, i.key_, hl.value from items_applications ia
inner join applications a on ia.applicationid = a.applicationid and ia.applicationid = 242
inner join items i on ia.itemid = i.itemid
inner join history_log hl on i.itemid = hl.itemid
where i.key_ l   |
+----------+----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

mysql> explain select ia.applicationid, ia.itemid, i.name, i.hostid, i.key_, hl.value from items_applications ia 
inner join applications a on ia.applicationid = a.applicationid and ia.applicationid = 242
inner join items i on ia.itemid = i.itemid and (i.key_ like 'log%' or i.key_ like 'logrt%')
inner join history_log hl on i.itemid = hl.itemid
order by ia.applicationid, ia.itemid, i.key_;
+----+-------------+-------+--------+-------------------------------------------+----------------------+---------+------------------+------+--------------------------+
| id | select_type | table | type   | possible_keys                             | key                  | key_len | ref              | rows | Extra                    |
+----+-------------+-------+--------+-------------------------------------------+----------------------+---------+------------------+------+--------------------------+
|  1 | SIMPLE      | a     | const  | PRIMARY                                   | PRIMARY              | 8       | const            |    1 | Using index              |
|  1 | SIMPLE      | ia    | ref    | items_applications_1,items_applications_2 | items_applications_1 | 8       | const            |    6 | Using where; Using index |
|  1 | SIMPLE      | i     | eq_ref | PRIMARY                                   | PRIMARY              | 8       | smp2rl.ia.itemid |    1 | Using where              |
|  1 | SIMPLE      | hl    | ref    | history_log_2,history_log_1               | history_log_2        | 8       | smp2rl.ia.itemid |  889 |                          |
+----+-------------+-------+--------+-------------------------------------------+----------------------+---------+------------------+------+--------------------------+
4 rows in set

mysql> 
mysql> explain select ia.applicationid, ia.itemid, i.name, i.hostid, i.key_, hl.value from items_applications ia 
inner join applications a on ia.applicationid = a.applicationid and ia.applicationid = 242
inner join items i on ia.itemid = i.itemid
inner join history_log hl on i.itemid = hl.itemid
where i.key_ like 'log%' or i.key_ like 'logrt%'
order by ia.applicationid, ia.itemid, i.key_;
+----+-------------+-------+--------+-------------------------------------------+----------------------+---------+------------------+------+--------------------------+
| id | select_type | table | type   | possible_keys                             | key                  | key_len | ref              | rows | Extra                    |
+----+-------------+-------+--------+-------------------------------------------+----------------------+---------+------------------+------+--------------------------+
|  1 | SIMPLE      | a     | const  | PRIMARY                                   | PRIMARY              | 8       | const            |    1 | Using index              |
|  1 | SIMPLE      | ia    | ref    | items_applications_1,items_applications_2 | items_applications_1 | 8       | const            |    6 | Using where; Using index |
|  1 | SIMPLE      | i     | eq_ref | PRIMARY                                   | PRIMARY              | 8       | smp2rl.ia.itemid |    1 | Using where              |
|  1 | SIMPLE      | hl    | ref    | history_log_2,history_log_1               | history_log_2        | 8       | smp2rl.ia.itemid |  889 |                          |
+----+-------------+-------+--------+-------------------------------------------+----------------------+---------+------------------+------+--------------------------+
4 rows in set