select * from means, it completely retrieves all the data
from database table. it is not good for programming.

select up to 1 row means, it retrieves all the related
values for that query.From that result first row is selected.

if we have primary key as where condition we can go for
select single.select single is not a loop operation.

Using Select single * we can get exact record as we are using 
primary key there,where as in Select up to 1 row,it will pick 
first record from the selected records.if we forgot to opt for  
primary keys in the where condition in select single then 
it'll act like select single up to 1 row.