It sounds like you need a program that monitors the serial port, formats the data, and writes a data file that can be read by Excel. One of the easiest paths is to create a comma delimited or comma separated value (CSV) file. These files can be directly opened by Excel and be imported into MySQL. A lot depends upon the nature of the serial data, but it isn’t hard to write a small program to do this. I’ve seen or written similar programs in C++, Java, Liberty BASIC, and PERL.
Another suggestion. Format your output as CSV. I do this with robotic telemetry and capture the output to file using hyper terminal. Then just open with Excel or OpenOffice.
Alternatively, there are free libs and compilers for C and Java.