बाएं बाहरी जॉइन की पहली पंक्ति प्राप्त करना

कोशिश करें DENSE_RANK रखें

डेटा स्रोत:

CREATE TABLE person
    (person_id int primary key, firstname varchar2(4), lastname varchar2(9))
/
INSERT ALL
    INTO person (person_id, firstname, lastname)
         VALUES (1, 'john', 'lennon')
    INTO person (person_id, firstname, lastname)
         VALUES (2, 'paul', 'mccartney')
SELECT * FROM dual;



CREATE TABLE address
    (person_id int, address_id int primary key, city varchar2(8))
/
INSERT ALL
    INTO address (person_id, address_id, city)
         VALUES (1, 1, 'new york')
    INTO address (person_id, address_id, city)
         VALUES (1, 2, 'england')
    INTO address (person_id, address_id, city)
         VALUES (1, 3, 'japan')
    INTO address (person_id, address_id, city)
         VALUES (2, 4, 'london')
SELECT * FROM dual;

प्रश्न:

    select  

      p.person_id, p.firstname, p.lastname,

      x.recent_city

    from person p
    left join (

        select person_id,      

            min(city) -- can change this to max(city). will work regardless of min/max

            -- important you do this to get the recent: keep(dense_rank last)

            keep(dense_rank last order by address_id) 
               as recent_city

        from address 
        group by person_id


    ) x on x.person_id = p.person_id

लाइव परीक्षण:http://www.sqlfiddle.com/#!4/7b1c9/ 2

Oracle के KEEP DENSE_RANK विंडोिंग फ़ंक्शन के साथ सभी डेटाबेस में समान कार्यक्षमता नहीं है, आप इसके बजाय सादे विंडोिंग फ़ंक्शन का उपयोग कर सकते हैं:

select  

  p.person_id, p.firstname, p.lastname,

  x.recent_city, x.pick_one_only

from person p
left join (

    select 

        person_id,      

        row_number() over(partition by person_id order by address_id desc) as pick_one_only,
        city as recent_city

    from address 



) x on x.person_id = p.person_id and x.pick_one_only = 1

लाइव परीक्षण:http://www.sqlfiddle.com/#!4/7b1c9/ 48

या टपल परीक्षण का उपयोग करें, उन डेटाबेस पर काम करेगा जो विंडोिंग फ़ंक्शन का समर्थन नहीं करते हैं:

select  

  p.person_id, p.firstname, p.lastname,

  x.recent_city

from person p
left join (

    select   
        person_id,city as recent_city    
    from address 
    where (person_id,address_id) in

          (select person_id, max(address_id)
           from address
           group by person_id)



) x on x.person_id = p.person_id 

लाइव परीक्षण:http://www.sqlfiddle.com/#!4/7b1c9/ 21

हालांकि सभी डेटाबेस पिछले कोड की तरह टपल परीक्षण का समर्थन नहीं करते हैं। आप इसके बजाय जॉइन का उपयोग कर सकते हैं:

select  

  p.person_id, p.firstname, p.lastname,

  x.recent_city

from person p
left join (

    select 

        address.person_id,address.city as recent_city

    from address 
    join 
    (
          select person_id, max(address_id) as recent_id
           from address
           group by person_id
    ) r 
    ON address.person_id = r.person_id
    AND address.address_id = r.recent_id



) x on x.person_id = p.person_id 

लाइव परीक्षण:http://www.sqlfiddle.com/#!4/7b1c9/ 24