[英]MYSQL FULL OUTER JOIN - All NULL results when using LEFT-UNION-LEFT JOIN
Tbl_A Tbl_A
cap_id| yr_a| sp_a| iso_a| area_a| qty_a | prod_a |
3| 2015| TRR| 54| 8| 120 | 0 |
678| 2015| BOM| 62| 27| 0.0 | 0 |
20| 2015| TRR| 54| 27| 0.0 | 0 |
45| 2015| FRC| 7| 15| 86800 | 0 |
52| 2015| AZB| 12| 6| 987 | 0 |
Tbl_B Tbl_B
aqua_id| yr_b| sp_b| iso_b| area_b| qty_b | prod_b |
78| 2015| OTS| 32| 27| 6868 | 1 |
333| 2015| FRC| 7| 15| 550 | 1 |
334| 2015| FRC| 7| 15| 550 | 2 |
789| 2015| TRR| 54| 27| 45000 | 3 |
987| 2015| TRR| 32| 27| 40 | 2 |
I got the FULL OUTER JOIN I was looking for 我得到了正在寻找的FULL OUTER JOIN
BUT the query is also generating a whole bunch of all NULL records (id's 7-9 in Tbl_C) 但是查询还会生成一堆所有的NULL记录(Tbl_C中的ID为7-9)
Tbl_C - Final Tbl Tbl_C-最终Tbl
id| cap_id| aqua_id| yr_a| yr_b| sp_a| sp_b| iso_a| iso_b|area_a|area_b| qty_a| qty_b | prod_a | prod_b
1 | 20| 789| 2015| 2015| TRR| TRR| 54| 54| 27| 27| 0.0| 45000 | 0 | 1
2 | 45| 333| 2015| 2015| FRC| FRC| 7| 7| 15| 15| 86800| 550 | 0 | 1
3 | 45| 334| 2015| 2015| FRC| FRC| 7| 7| 15| 15| 86800| 550 | 0 | 2
4 | 678| NULL| 2015| NULL| BOM| NULL| 62| NULL| 27| NULL| 0.0| NULL | 0 | NULL
5 | 3| NULL| 2015| NULL| TRR| NULL| 54| NULL| 8| NULL| 120| NULL | 0 | NULL
6 | NULL| 78| NULL| 2015| NULL| OTS| NULL| 32| NULL| 27| NULL| 6868 | 0 | 1
7 | NULL| 987| NULL| 2015| NULL| TRR| NULL| 32| NULL| 27| NULL| 40 | 0 | 2
8 | NULL| NULL| NULL| NULL| NULL| NULL| NULL| NULL| NULL| NULL| NULL| NULL | NULL | NULL
9 | NULL| NULL| NULL| NULL| NULL| NULL| NULL| NULL| NULL| NULL| NULL| NULL | NULL | NULL
I'm trying to work out what is causing the extra multiple all NULL records? 我正在尝试找出是什么原因导致所有NULL记录额外增加?
The query used was: 使用的查询是:
(SELECT a.cap_id, b.aqua_id, a.yr_a, b.yr_b,...., a.qty_a, b.qty_b
FROM Tbl A AS a LEFT JOIN Tbl_B AS b
ON a.yr_a = b.yr_b
AND a.iso_a = b.iso_b
AND a.area_a = b.area_b
AND a.sp_a = b.sp_b
WHERE a.yr_a = 2015)
UNION
(SELECT a.cap_id, b.aqua_id, a.yr_a, b.yr_b,...., a.qty_a, b.qty_a
FROM Tbl_B AS b LEFT JOIN Tble_A AS a
ON a.yr_a = b.yr_b
AND a.iso_a = b.iso_b
AND a.area_a = b.area_b
AND a.sp_a = b.sp_b
WHERE b.yr_b = 2015);
DEMO: http://rextester.com/AWDYA21027 using your sample data & query I don't get the repeated null columns. 演示: http : //rextester.com/AWDYA21027使用您的示例数据和查询我没有得到重复的空列。 This implies a data issue.
这意味着存在数据问题。
Why make it a left join? 为什么要左联接? Just switch left to right and the where clause to b.yr_a.
只需从左切换到右,将where子句切换到b.yr_a。
and to eliminate the nulls ensure at least one of the join criteria match by eliminating records who have all 4 values null? 并通过消除所有四个值都为空的记录来确保至少有一个联接条件匹配,以消除空值?
Given your sample data a full outer join would return: when ordered by cap_Id and aqua_ID 给定您的样本数据,将返回完整的外部联接:按cap_Id和aqua_ID排序时
+--------+---------+------+------+-------+-------+
| CAP_ID | AQUA_ID | YR_A | YR_B | QTY_A | QTY_B |
+--------+---------+------+------+-------+-------+
| | 78 | | 2015 | | 6868 |
| | 987 | | 2015 | | 40 |
| 3 | | 2015 | | 120 | |
| 20 | 789 | 2015 | 2015 | 0 | 45000 |
| 45 | 333 | 2015 | 2015 | 86800 | 550 |
| 678 | | 2015 | | 0 | |
+--------+---------+------+------+-------+-------+
The below query returns: 以下查询返回:
+----+--------+---------+------+------+----------+----------+
| | cap_id | aqua_id | yr_a | yr_b | qty_a | qty_b |
+----+--------+---------+------+------+----------+----------+
| 1 | NULL | 78 | NULL | 2015 | NULL | 6868,00 |
| 2 | NULL | 987 | NULL | 2015 | NULL | 40,00 |
| 3 | 3 | NULL | 2015 | NULL | 120,00 | NULL |
| 4 | 20 | 789 | 2015 | 2015 | 0,00 | 45000,00 |
| 5 | 45 | 333 | 2015 | 2015 | 86800,00 | 550,00 |
| 6 | 678 | NULL | 2015 | NULL | 0,00 | NULL |
+----+--------+---------+------+------+----------+----------+
Which seems to be the correct results for a full outer join. 对于完全外部联接,这似乎是正确的结果。 if I have duplicate values in A or B, this query returns those duplicates since the distinct in the UNION is not occurring as we are doing a union all;
如果我在A或B中有重复的值,则此查询将返回这些重复的值,因为UNION中的区别不会出现,因为我们正在做一个并集。 not a union.
不是工会。
(SELECT a.cap_id, b.aqua_id, a.yr_a, b.yr_b, a.qty_a, b.qty_b
FROM tbl_A AS a
LEFT JOIN tbl_B AS b
ON a.yr_a = b.yr_b
AND a.iso_a = b.iso_b
AND a.area_a = b.area_b
AND a.sp_a = b.sp_b
WHERE a.yr_a = 2015
and (a.yr_a is not null
or a.iso_a is not null
or a.area_a is not null
or a.sp_a is not null))
UNION ALL
(SELECT a.cap_id, b.aqua_id, a.yr_a, b.yr_b, a.qty_a, b.qty_b
FROM tbl_A AS a
RIGHT JOIN tbl_B AS b
ON a.yr_a = b.yr_b
AND a.iso_a = b.iso_b
AND a.area_a = b.area_b
AND a.sp_a = b.sp_b
WHERE b.yr_b = 2015
and (b.yr_b is not null
or b.iso_b is not null
or b.area_b is not null
or b.sp_b is not null)
and a.iso_a is null #to exclude extra nulls duplicated by union all.
);
NULLS were generated because: Without a "IS NULL" in the WHERE clause for one of the ON clause variables in the second LEFT JOIN the INNER JOIN runs twice! 生成NULL的原因是:在第二个LEFT JOIN的ON子句变量之一的WHERE子句中没有“ IS NULL”的情况下,INNER JOIN运行了两次! Exacerbated by fact that I was left joining a shorter table to a longer one (row_# for Tbl_B < Tbl_A), so no record existed in Tbl_b for all Tbl_A 2015 records.
事实上,由于我只剩下一个较短的表和一个较长的表(Tbl_B <Tbl_A的row_#),所以事实变得更糟,因此所有Tbl_A 2015记录的Tbl_b中都没有记录。
The answer seems to be quite simple. 答案似乎很简单。 If you take the 1st select and run it:
如果选择第一个选择并运行它:
SELECT a.*, b.*
FROM Tbl_A AS a LEFT JOIN Tbl_B AS b
ON a.yr_a = b.yr_b
AND a.iso_a = b.iso_b
AND a.area_a = b.area_b
AND a.sp_a = b.sp_b
WHERE a.yr_a = 2015
you should probably get 5 result lines as 5 lines are of the Tbl_A. 您可能应该获得5条结果行,因为5条行属于Tbl_A。 The problem is that not all of these lines joins with lines in the Tbl_B due to the join criteria.
问题是由于联接条件,并非所有这些行都与Tbl_B中的行联接。 As such when you join these tables, for some rows of Tbl_A, there will be columns of Tbl_B that will be NULL as the join is Outer.
这样,当您连接这些表时,对于Tbl_A的某些行,由于连接为外部,因此Tbl_B的列将为NULL。
The same applies to your second Query too: 同样适用于第二个查询:
SELECT a.*, b.*
FROM Tbl_B AS b LEFT JOIN Tbl_A AS a
ON a.yr_a = b.yr_b
AND a.iso_a = b.iso_b
AND a.area_a = b.area_b
AND a.sp_a = b.sp_b
WHERE b.yr_b = 2015
Rows from Tbl_B do not have an exact join with Tbl_A and as such since you left join to B, you will have lines of the Tbl_B that have plenty of NULLs. 来自Tbl_B的行没有与Tbl_A完全连接,因此,自从您离开对B的连接以来,您将在Tbl_B的行中包含大量NULL。
I would advice you to run them 1 by one and see the results of each query. 我建议您一个接一个地运行它们,并查看每个查询的结果。
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