[Nero_3D]

arrays are always transfered to a function by reference
normal variables are normally transfered by value, add a & in front of it to make it by reference

pawn Код:

stock GetMyString(array[]) array = "Added";
// /\ if that does give an error use that \/
stock GetMyString(array[], const size = sizeof array) strcat((array[0] = EOS, array), "Added", size);

pawn Код:

new Text[16];
GetMyString(Text);
print(Text); // prints Added

For your other problem use mysql_get_field(const fieldname[], string[])