postgresql - in SQL, best way to join first and last instance of child table without NOT EXISTS? -


in postgresql, have issue table , child issue_step table - issue contains 1 or more steps.

the view issue_v pulls things issue , first , last step: author , from_ts pulled first step, while status , thru_ts pulled last step.

the tables

create table if not exists seeplai.issue(   isu_id      serial        primary key,   subject       varchar(240) ); create table if not exists seeplai.issue_step(   stp_id      serial        primary key,   isu_id      int           not null references seeplai.issue on delete cascade,   status      varchar(12)   default 'open',   stp_ts      timestamp(0)  default current_timestamp,   author      varchar(40),   notes       text );

the view

create view seeplai.issue_v select isu.*,       first.stp_ts from_ts,       first.author author,       first.notes notes,       last.stp_ts thru_ts,       last.status status  seeplai.issue isu join  seeplai.issue_step first on( first.isu_id = isu.isu_id , not exists(       select 1 seeplai.issue_step isu_id=isu.isu_id , stp_id>first.stp_id ) ) join  seeplai.issue_step last on( last.isu_id = isu.isu_id , not exists(         select 1 seeplai.issue_step isu_id=isu.isu_id , stp_id<last.stp_id    ) );

note1: issue_step.stp_id guaranteed chronologically sequential, using instead of stp_ts because it's indexed

this works, ugly sin, , cannot efficient query in world.

in code, use sub-query find first , last step ids, , join 2 instances of step table using found values.

select  isu.*         ,s1.stp_ts from_ts         ,s1.author author         ,s1.notes notes         ,s2.stp_ts thru_ts         ,s2.status status    seeplai.issue isu inner join     (     select  isu_id             ,min(stp_id) min_id             ,max(stp_id max_id        seeplai.issue_step     group             isu_id     ) sq on  sq.isu_id = isu.isu.id inner join         seeplai.issue_step s1 on      s1.stp_id = sq.min_id inner join         seeplai.issue_step s2 on      s2.stp_id = sq.max_id

note: shouldn't using select * in view. better practice list out fields need in view explicitly


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