The optimization process and recommendations:

1. Avoid Calling Functions With Indexed Columns (query line: 14): When a function is used directly on an indexed column, the database's optimizer won’t be able to use the index. For example, if the column `datea` is indexed, the index won’t be used as it’s wrapped with the function `trunc`. If you can’t find an alternative condition that won’t use a function call, a possible solution is to store the required value in a new indexed column.
2. Avoid Calling Functions With Indexed Columns (query line: 16): When a function is used directly on an indexed column, the database's optimizer won’t be able to use the index. For example, if the column `date` is indexed, the index won’t be used as it’s wrapped with the function `trunc`. If you can’t find an alternative condition that won’t use a function call, a possible solution is to store the required value in a new indexed column.
3. Avoid Correlated Subqueries (query line: 8): A correlated subquery is a subquery that contains a reference (column: date) to a table that also appears in the outer query. Usually correlated queries can be rewritten with a join clause, which is the best practice. The database optimizer handles joins much better than correlated subqueries. Therefore, rephrasing the query with a join will allow the optimizer to use the most efficient execution plan for the query.

The optimized query:

SELECT
        a.date,
        (a.counter1 + c.counter) / (c.counter1 - a.counter1) percentdiferent 
    FROM
        dailytable a 
    JOIN
        (
            SELECT
                trunc(b.date) date,
                sum(counter1) counter1 
            FROM
                minutetable b 
            WHERE
                trunc(b.datea) = a.date 
            GROUP BY
                trunc(b.date)
        ) c 
            ON c.date = a.date 
            AND c.counter1 <> a.counter1 
    WHERE
        percentdiferent > 5