num_rows returning empty while result_array has results

while I was testing my registration system, I've created a lot of entries in a database. then I deleted it but I still see all the rows in the query result.

In other words. I am having a result different then the data in the database. I am still seing previously deleted results.

How can I work properly with cash so this don't happend. Where can I learn about the way Codeigniter 3 caches query results?

Thanks.