CODEWITHSUNDEEP
sqloracle-databaseouter-join
Peter Lang
Peter Lang

Reputation: 55584

Getting only one row in outer join using oracle

I've got a table and want to outer-join another table, getting only the first row (the one with lowest nr) of the second table using Oracle 10g.

Edit: nr is unique within an id

Table x    Table y
id         id  nr  code
 1          1   1   B
 2          1   2   A
 3          2   2   A

Expected result:
id   nr     code
 1    1      B
 2    2      A
 3    NULL   NULL

Example with test data (does not do the limitation to single row but should allow faster testing):

WITH
  x AS( SELECT 1 id FROM dual UNION SELECT 2 FROM dual UNION SELECT 3 FROM dual ),
  y AS( SELECT 1 id, 1 nr, 'B' code FROM dual
        UNION SELECT 1, 2, 'A'  FROM dual
        UNION SELECT 2, 2, 'A' FROM dual
) -- end of test data
SELECT x.id, y.nr, y.code
  FROM x
  LEFT OUTER JOIN y ON ( y.id = x.id )

Upvotes: 2

Views: 13737

Answers (2)

CoolMagma
CoolMagma

Reputation: 

WITH
  x AS( SELECT 1 id FROM dual UNION SELECT 2 FROM dual UNION SELECT 3 FROM dual ),
  y AS( SELECT 1 id, 1 nr, 'B' code FROM dual
        UNION SELECT 1, 2, 'A'  FROM dual
        UNION SELECT 2, 2, 'A' FROM dual
) -- end of test data
SELECT x.id, y.nr, y.code
  FROM x
  LEFT OUTER JOIN y ON ( y.id = x.id )
WHERE rownum = 1 --Add this

Upvotes: 0

Quassnoi
Quassnoi

Reputation: 425613

WITH
  x AS( SELECT 1 id FROM dual UNION SELECT 2 FROM dual UNION SELECT 3 FROM dual ),
  y AS( SELECT 1 id, 1 nr, 'B' code FROM dual
        UNION SELECT 1, 2, 'A'  FROM dual
        UNION SELECT 2, 2, 'A' FROM dual
) -- end of test data
SELECT  *
FROM    (
        SELECT  x.id, y.nr, y.code, ROW_NUMBER() OVER (PARTITION BY x.id ORDER BY y.nr) AS rn
        FROM    x
        LEFT OUTER JOIN y
        ON   y.id = x.id
)
WHERE rn = 1

Upvotes: 13

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