Before I start replying to your question I feel it is important to mention that I am not a lawyer. My reply is only my interpretation of how MySQL handles their licencing.
My understanding is that if you bundle MySQL with your app you should pay MySQL for each app you sell. If you on the other hand instruct your customer(s) to download and install MySQL themselves before they install your app you should not have to pay MySQL.
Again this is just my $0.02 and should not be considdered legal advise.

Einar

>Hi,
>
>I am confused on the following issues on Open source software
>
>* If I get Mysql for use with my own written application.
>When my customer purchased my software and want to use MySql
>in their company, do my customer had to pay for the use of MySql ?
>
>My friend told me that my customer don't had to pay for it as
>I thought my customer had to pay for it as they are using for
>their company use for profit. Please correct me on the above
>issue.