That Query works NO MATTER WHAT YOU THINK. Please care enough to run and check rather than making statement based on instincts. There are a lot more things in DB2 than what me or you can think. Use the query for your benefit or don't but don't give out verdicts based on your thoughts.
1) how can you put column from table1 without joining it with table2
2) After join also how will this query verify that this is updating Right row of the table1
Good questions. Have you ever heard of the term subquery? If not, its time to learn them.
Please go thru the link if you really care enough to learn.