SQL query suggestions please - mysql

Question

I'm trying to write a SQL query to calculate prices for licenses.
Please check the schema below:
Table: Prices
| ID (bigint) | USERS(Bigint) | TYPE (varchar) | PRICE (BIGINT)
------------------------------------------------------------------
| 1 | 1 | other | 20 |
| 2 | 15 | local | 13.96 |
Table: Licenses
| ID (bigint) | USERID (Bigint) |STATUS(VARCHAR) | USERS(bigint) | DEVICES(BIGINT) | TYPE(VARCHAR) | REQUEST_TYPE (VARCHAR) |
--------------------------------------------------------------------------------------------------------------
| 1 | 13 | 10 | 10 | local | add |
| 2 | 13 | 15 | 20 | other | extend |
My objective:
Given a userid and type, i want to calculate total prices of all the licenses of basing on following critirea:
For given userid and type:
1) Get all licenses which have request_type as either new (or) extend
2) For each such license, match the number of users (USERS column) with USERS column from 'prices' table and do calculation as devices*(associated price from prices table)
3) Using this calculate sum of all such prices and return a total price.
I'm trying to do this by using the following query but i'm not successful yet:
SELECT SUM(PRICE) FROM prices
LEFT OUTER JOIN licenses
ON (
prices.users=licenses.users
AND prices.type=licenses.type
)
WHERE licenses.userid=13
AND licenses.status='approved'
AND licenses.request_type IN ('add','extend')
Please check SQL Fiddle here: http://sqlfiddle.com/#!2/05f5cf
Pleas help.
Thanks,
David

Answer 1

the result will be null, because query cannot found the condition of LEFT OUTER JOIN
there is the query
SELECT SUM(PRICE) FROM prices
LEFT OUTER JOIN licenses
ON (
prices.users=licenses.users
AND prices.type=licenses.type //cannot found condition on table
)
WHERE licenses.userid=13
AND licenses.status='approved'
AND licenses.request_type IN ('add','extend')
in this is the data inside table
table licences
(1, 'approved', 10, 10, 'local', 'add', 13),
(2, 'approved', 15, 20, 'other', 'extend', 13);
and table prices
(1, 1, 'other', 20),
(2, 15, 'local', 13.96);
and your condition is
prices.users=licenses.users
AND prices.type=licenses.type //cannot found condition on table
that mean if from your table is
at licences table have a type="other" and users=15
but at prices table haven't have type="other" and users=15
so the result will be null
because when i change the first row of table prices
(1, 1, 'other', 20)
becomes (1, 15, 'other', 20),
that will be have a result = 20
you need change your first line of query
SELECT SUM(PRICE) FROM prices
be
SELECT IFNULL(SUM(PRICE),0) FROM prices
this will change the result if haven't found the row to 0 not null

Answer 2

From your comments and updates, I think you want (not sure if it's necessary to compare users in license and users in price, but it seems youd want this)
select coalesce(sum( p.users * p.price), 0)
FROM licenses l
inner join prices p
on p.type = l.type
--and p.users = l.users
where l.status = 'approved'
and l.request_type in ('add', 'extend')
and l.userid = 13
Edit
In fact, do you need to check that type AND users are identical, or just users ?
If you need only check on users, then
inner join prices p
on p.users = l.users
If you need only check on type
inner join prices p
on p.type = l.type
If you need both, you will get 0 with your sample datas.
See SqlFiddle with 3 versions.