[pguser]

test=*# select * from maschine ;
  nu   |   datum    | artikel
-------+------------+---------
 12345 | 2014-05-21 |  444444
(1 row)

Time: 0,131 ms
test=*# select * from zaehler ;
 m_nu  |   datum    | zaehler
-------+------------+---------
 12345 | 2014-04-15 |  545454
 12345 | 2014-08-08 |  777777
(2 rows)

Time: 0,135 ms
test=*# select m.*, z.*, abs(m.datum-z.datum) from maschine m left join zaehler z on m.nu=z.m_nu order by abs(m.datum-z.datum);
  nu   |   datum    | artikel | m_nu  |   datum    | zaehler | abs
-------+------------+---------+-------+------------+---------+-----
 12345 | 2014-05-21 |  444444 | 12345 | 2014-04-15 |  545454 |  36
 12345 | 2014-05-21 |  444444 | 12345 | 2014-08-08 |  777777 |  79
(2 rows)

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