Question

我正在尝试加入两个表ORDER和ORDER_FLG。我想从ORDER中提取所有列，而不是将Flg作为＆＃39; Y＆＃39;在ORDER_FLG表中。

ORDER

Branch_nbr |Order_Id | Order_start_dt |Order_end_dt 
0001    | 110000   | 01/01/2014 | 02/02/2014
0002    |   110001  |  03/03/2014  |  04/04/2014
0003    |   110002  |   05/05/2014  |  06/06/2014

ORDER_FLG

Branch_Nbr |Order_Id |Flg
0001    |   110000| Y
0003    |   110002| N

SQL：

SELECT A.*
FROM ORDER AS A LEFT JOIN ORDER_FLG AS B
ON A.Branch_nbr=B.Branch_nbr AND A.Order_Id=B.Order_Id
WHERE A.Order_start_dt >= 'SOME_DATE'
AND A.Order_end_dt <= 'SOME_DATE'
AND B.Flg <> 'Y'

我应该得到两行（110002,110001）作为输出，但我只得到一行。如果第二个表中不存在条目，则不从第一个表中提取数据。不应该从第一个表中拉出所有数据吗？

我尝试了这个，它有效但需要时间 -

SELECT A.*
FROM ORDER AS A 
WHERE A.Order_start_dt >= 'SOME_DATE'
AND A.Order_end_dt <= 'SOME_DATE'
AND A.Order_Id NOT IN ( SELECT Order_Id FROM ORDER_FLG
WHERE Order_Id=A.Order_Id AND Branch_nbr=A.Branch_nbr 
AND Flg='Y')

Answer 1

您的where子句包含对外表的引用： AND B.Flg <> 'Y'

在外连接之后应用where子句。来自外部联接表的任何不具有匹配项的行将在结果集中具有空值。 Null与您的约束不匹配，因此从结果集中删除行。

Try this instead:
SELECT A.*
FROM ORDER AS A LEFT JOIN ORDER_FLG AS B
ON A.Branch_nbr=B.Branch_nbr AND A.Order_Id=B.Order_Id
AND B.Flg <> 'Y' 
WHERE A.Order_start_dt >= 'SOME_DATE'
AND A.Order_end_dt <= 'SOME_DATE'

Answer 2

试试这个：

SELECT A.*
FROM ORDER AS A LEFT JOIN ORDER_FLG AS B
ON A.Branch_nbr=B.Branch_nbr AND A.Order_Id=B.Order_Id
WHERE A.Order_start_dt >= 'SOME_DATE'
AND A.Order_end_dt <= 'SOME_DATE'
AND (B.Flg IS NULL OR B.Flg <> 'Y' )

B.Flg＆lt;＆gt; ＆＃39; Y＆＃39;对于在ORDER_FLG中没有匹配行的所有订单，条件显然是假的。在这些字段中得到NULL，因此必须在WHERE子句中允许这种可能性。

左连接 - 连接两个表并从左表中提取所有数据

2 个答案: