How do I retrieve items that have changed their value type?

[Cesar Murilo Cesar]

In the Zabbix monitoring system database, we have the itemid and history table. The whole scheme can be seen through the link below:

https://zabbix.org/mw/images/a/ad/Zabbix_db_schema-2.4.3-MySQL.pdf

It turns out that for a long time, we monitor the internet band the wrong way, but now that we have adjusted the item, the past graphics no longer appear. And I wanted to correct the values ​​manually by multiplying them by 8 (to turn byte into bits) and adjusting to the correct type unsigned numeric (before was numeric float).

Only I can't retrieve the values ​​if I change the item type. The query is: select history.value where itemid = '28608';

From the moment I change to the unsigned type, select in the history table only returns me the records that conform to the value_type 3 (unsigned).

But the records are not deleted, if I return the type to float, it shows the records that were saved as float, consequently I also see the graphics.