select - SQL SUM restricted -

i have view pulling data number of tables. let's consider this:

 transpk   amount    currency_id  -------------------------------  1         2000      0  1         -2000     0  2         3600      1  2         -7200     2  . . . 

i want calculate sum(amount), per distinct transpk, currency_ids given transpk same. i.e. in data above there 1 result returned, since transpk=2 there 2 values currency_id.

i have no idea search on this! i've tried "sql sum restricted", hits weren't useful. i'm not first person want this. able point me in right direction?

try this:

select transpk, sum(amount) tablea  group transpk having count(distinct currency_id) = 1; 

check sql fiddle demo

output

| transpk | amount | |---------|--------| |       1 |      0 | |       3 |   3000 |