Oracle SQL Tips

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左串連的同時只輸出關聯表的一條記錄

WITH X AS

(SELECT1IDFROM DUAL UNIONSELECT2FROM DUAL UNIONSELECT3FROM DUAL),

Y AS

(SELECT1ID, 1 NR, ‘B‘CODE

FROM DUAL

UNION

SELECT1, 2, ‘A‘

FROM DUAL

UNION

SELECT2, 2, ‘A‘

FROM DUAL) -- end of test data

SELECT *

FROM (SELECT X.ID,

Y.NR,

Y.CODE,

ROW_NUMBER() OVER(PARTITIONBY X.ID ORDERBY Y.NR) AS RN

FROM X

LEFTOUTERJOIN Y

ON Y.ID = X.ID)

WHERE RN = 1

結果如下：

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