their should be a relationship between the tables then only 
we can use join conditions....
But the subquery can be used to retrive data from one or 
more table if their is no relation between the tables....

Majorly subqueries  run independently and result of the
subquery used in the outer query(other than corelated subquery).
And in case of join a query only give the result when the
joining condition gets satisfied.

Join:
It is the method of joining one or more tables together and 
finding a answer.

Sub Query:

It is a method of finding one answer using another query.

Main Difference:

In join both the tables should have a comman column name
but in subquery without having a column name we can execute 
the query.

Join:
It is the machanism of joining one or more tables together 
and finding information from one or all tables used in join.

Sub Query:

It is a method of finding answer using another query as 
parametere for first query.

Main Difference:

In join both the tables should have a comman column type
but in subquery without having a column type we can execute 
the query.

Sub Query:

The Sub Query only get the results as one table or the 
other table based that the result be of onther table as 
used in the table.
The two tables information are dispalyed as combiend.

Join:
 
To get results more rhan two tables information.

their should be a relationship between the tables then only 
we can use join conditions....
But the subquery can be used to retrive data from one or 
more table if their is no relation between the tables....

The main difference between join and sub query is :
join is used to retrieve data from two different tables 
where as in sub query we can retreive data from one table 
using the result of the where condition on another table.

join combines tables and retrieves data where as sub query 
doesn't combines two table.join is more faster than subquery

the main diff is
 
the subquery gives the result from one table only,but whose condition may depend on another table i.e the inner query.

whereas join gives the result from both the tables if condition is satisfied

main difference between join and subqurey  is that join is
used for known condition while subquery is used for unknown
condition.