Oracle SQL Tips

左连接的同时只输出关联表的一条记录

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

结果如下：

ID	NR	CODE	RN
1	1	B	1
2	2	A	1
3			1