(Oracle SQL) Problems with joins and pairs of rows -

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i have 3 tables

create table airships(     idas number primary key,     nameas varchar2(20),     range number                      );  create table certificate(       idem number not null,       idas number not null,       foreign key (idem) references employees(idem),       foreign key (idas) references airships(idas)                         );   create table employees(       idem number primary key,       nameem varchar2(20),       paycheck number                     );

i have find pairs of employees certified same airships range on 3000.

i know have use join, dont know how find pairs same table.

select e1.nameem, e2.nameem, a.nameas employees e1 join certificates c1 on e1.idem = c1.idem join certificates c2 on c1.idas = c2.idas , c1.idem < c2.idem join employees e2 on e2.idem = c2.idem join airships on a.idas = c1.idas a.range > 3000

the c1.idem < c2.idem test keeps reporting employee pair himself, , avoids showing same pair twice (in opposite order).


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