sql query to link two tables - sql

Question

I have a table called users where the employee data are stored.
Also I have another table payment_details where employee's payment related data are stored
the two tables are as follows.
this table is users
sr_no emp_no username payment
1 1001 leroy <null>
2 1003 harry <null>
3 1004 Tom <null>
4 1008 Jon <null>
This table below is payment_details
sr_no name number month status date
43 Jon 1008 January paid 5/16/2012
44 Jon 1008 January balance 5/16/2012
45 Harry 1003 January paid 5/16/2012
46 Tom 1004 January paid 5/16/2012
47 leroy 1001 January paid 5/16/2012
48 Jon 1008 January paid 5/16/2012
49 Harry 1003 January paid 5/16/2012
50 Jon 1008 February balance 5/16/2012
51 leroy 1001 February paid 5/16/2012
52 Jon 1008 February paid 5/16/2012
53 Tom 1004 February balance 5/16/2012
My question here is to update "users" table payment column to "paid" when the status of his/her is all paid in payment_details table

Answer 1

You can either do this: http://www.sqlfiddle.com/#!3/db13f/18
update users set payment = 'paid'
from
(
select number
from payment_details
group by number
having sum(case when status = 'paid' then 1 end)
= count(*)
) as x
where x.number = users.emp_no;
Or this: http://www.sqlfiddle.com/#!3/db13f/19
update users
set payment = x.upd
from
(
select u.emp_no,
case when sum(case when d.status = 'paid' then 1 end) = count(*) then
'paid'
else
null
end as upd
from users u
left join payment_details d
on d.number = u.emp_no
group by u.emp_no
) as x
where x.emp_no = users.emp_no;
Their difference is how many rows it updates. On the second query, it updates all users, regardless if the user has a paid all status('paid') or not(null); on the first query, it updates only those who are paid.
The advantage of the second query, is when you change one of the all 'paid' status on payment_detail of a given user to 'not paid' for example, it can revert back the user's payment status to null

Answer 2

UPDATE order_details
SET payment= 'paid'
WHERE not EXISTS (SELECT 1
FROM payment_details
WHERE payment_details.emp_no= order_details.emp_no
AND payment_details.status <> 'paid'
)

Answer 3

There also simple way to get the value of particulars table into variable and update the tabe as below:
declare #bb varchar(50)
select #bb= status from payment_details where name=#name and id=#id
update uuser set payment = #bb
where name = #name and id=#id