When my query finishes there is a message at the bottom of the MySQL browser:

5000 rows fetched in 0.68s (3.0988s)

What does this mean?

It seemed to me that the query used 3 seconds but why the number 0.68s?

Sometimes I see this kind of message:

50000 rows fetched in 8.68s (0.388s)

the first number is bigger.

Thanks.

Probably run time vs. real time. Explanation: if a process used 50% of the CPU for 10 seconds, it is said to have used 5 seconds of run time but 10 seconds of real time. (Different people have different terms for these concepts, btw.)

Database operations tend to wait a lot for IO, so they rarely fully utilize the CPU.