Well, you knew exactly what you needed when you created a table. Only now when you created a child table, the child table does not update with the information from your main table. Or worse you deleted something from your primary table and it still lives in the child table. You need a foreign key, my friend. This is how you define one after you've created your table.
ALTER TABLE My_Child_Table ADD CONSTRAINT FK_User_ID
FOREIGN KEY ( User_ID_In_Child_Table )
REFERENCES My_Primary_Table ( User_ID_In_Primary_Table )
ON DELETE CASCADE
ON UPDATE CASCADE
The last two lines are important. In this example, if the user id in the primary table is modified or deleted, the change will cascade to the child table. This ensures consistency between the two tables.
As always, this works on SQL Server. Check your documentation for mySql, Oracle, etc.
So, you made an awesome function that does cool things. Only the return type is a double and you have to display it as a string. No problem, you'll just have to convert it using this little snippet:
String my_String_for_Display = new String();
my_String_for_Display = Double.toString(my_Function());
This should would for C# as well, with minor modifications, but check the MSDN pages. This will also work for a double value instead of a function call, function with parameters, etc.
