两个表的SQL总和

Question

I have these two tables:

I need to join the payment table with the discount table. The expected output seems not possible since the discounts table doesn't have a payment date. I can only get the net_amount

payment table:
id    |  net_amount  |  payment_dt  |  person_id
1001  |  2765.36     |  2016-05-28  |  372
1002  |  2474.76     |  2016-05-29  |  372
1003  |  22694.25    |  2016-05-29  |  384
1004  |  1911.92     |  2016-05-29  |  384

discounts table:
id |  person_id  |  gross_amount | sc_discount | other_discount_amount | other_discount_type
1  |  372        |  3566.7       | 713.34      | 88.00                 | MISC 
2  |  372        |  3202.2       | 640.44      | 87.00                 | PAT
3  |  384        |  3566.7       | 713.34      | 285.34                | MISC
4  |  384        |  27953.10     | 5590.62     | 2236.25               | PAT
5  |  384        |  2655.45      | 531.09      | 212.44                | MISC

*1 - payment_dt is 2016-05-28

expected output: (where payment_dt=2016-05-29)
total_gross_amount | total_sc_discount | total_misc_discount | total_pat_discount | total_net_amount
37,377.45          | 7475.49           | 497.78              | 2,323.25           | 27,080.93

Answer 1

As I see in both tables common column is person_id, you can try to join with it. And for more information you can have in mind natural joins, read about it on The Internet ;)

"A NATURAL JOIN is a JOIN operation that creates an implicit join clause for you based on the common columns in the two tables being joined. Common columns are columns that have the same name in both tables. A NATURAL JOIN can be an INNER join, a LEFT OUTER join, or a RIGHT OUTER join. The default is INNER join. "

Answer 2

By assuming : net_amount = gross_amount - sc_discount - other_discount_amount

You do not need to go to payments table for total_net_amount in the expected output

You can write it like this :

Select sum(gross_amount)  as total_gross_amount,
sum(sc_discount) as total_sc_discount,
sum(gross_amount - sc_discount - other_discount_amount) as total_net_amount
sum(CASE other_discount_type when 'MISC' THEN other_discount_amount WHEN 'PAT' THEN 0) as total_misc_discount,
sum(CASE other_discount_type when 'MISC' THEN 0 WHEN 'PAT' THEN other_discount_amount) as total_pat_discount    
from discounts

And in case the above assumption is not true, As the aggregation is complete, only 1 row will come in output, you can get all columns except total_net_amount as in above query, get sum(net_amount) from payments table, and join them on true as only 1,1 row.