[英]Postgresql SELECT LEFT JOIN with columns on case
SELECT a1,a2,a3,a4,count(a5),b1,b2,b3
FROM table1
LEFT JOIN table2 ON a1=b1 AND a2=b2 (*here i need to join
next columns a3=b3 only if from table2 will be returned more than 1 records
other wise first 2 columns will be enough*)
group by a1,a2,a3,a4,a5,b1,b2,b3
有人知道如何执行此技巧吗?
好吧,如果我正确理解:
FROM table1 t1 LEFT JOIN
(SELECT t2.*, COUNT(*) OVER (PARTITION BY b1, b2) as cnt
FROM table2 t2
)
ON t1.a1 = t2.b1 AND t1.a2 = t2.b2 AND
(cnt = 1 OR t1.a3 = t2.a3)
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