all objects join and Crl-A ? in 2.5

any idea how to do this in script to Ctrl-A all the objects ?
and then join objects one after antoher one in a loop after creating one object

cause i would be prefer to jon theses automatically that would be a lot faster then doing it manually !

i found theses 2 for join

but what is the differences

Join selected objects into active object

and this other one


Merge selected objects to shapes of active object

so what the difference here ?

and any equivalent in BPY.TYPEs ?

Thanks & happy 2.5