[英]SQL Select Statement: One Child - Two Parents (two different FK)
I have the situation where the best to explain it is through the following scenario: 我遇到的情况最好通过以下情况来解释:
Child
record has two Parent
s (Mother and Father) Child
记录有两个Parent
(母亲和父亲)的地方 If you later to read this post consider the option to apply the self-referencing tables
scenario, it is not necessary, there are no neither grandfathers nor grandsons. 如果您以后要阅读此文章,请考虑应用self-referencing tables
方案的选项,则没有必要,既没有祖父也没有孙子。
About the parent it is defined how: 关于父级 ,定义方式:
CREATE TABLE IF NOT EXISTS parent(
code varchar(3),
name varchar(10),
PRIMARY KEY(code)
)ENGINE=INNODB;
The records are inserted how: 记录如何插入:
INSERT INTO parent(code,name) VALUES('001','Mary');
INSERT INTO parent(code,name) VALUES('002','Joseph');
INSERT INTO parent(code,name) VALUES('003','Adan');
INSERT INTO parent(code,name) VALUES('004','Eva');
INSERT INTO parent(code,name) VALUES('005','Ana');
INSERT INTO parent(code,name) VALUES('006','Elcana');
And the select
query works how is expected: select
查询的工作方式如何:
mysql> select * from parent;
+------+--------+
| code | name |
+------+--------+
| 001 | Mary |
| 002 | Joseph |
| 003 | Adan |
| 004 | Eva |
| 005 | Ana |
| 006 | Elcana |
+------+--------+
6 rows in set (0.01 sec)
About the child it is defined how: 关于孩子,它定义了如何:
CREATE TABLE IF NOT EXISTS child(
code varchar(3),
name varchar(10),
PRIMARY KEY(code),
mother_code varchar(3),
father_code varchar(3),
FOREIGN KEY fk_mother_code(mother_code) REFERENCES parent(code),
FOREIGN KEY fk_father_code(father_code) REFERENCES parent(code)
)ENGINE=INNODB;
Observation: from above observe the Child
expects two PK
s from the Parent
(assume that must be different) through two FK
s. 观察:从上面观察, Child
期望Parent
通过两个FK
来获得两个 PK
(假定必须不同)。
The records are inserted how: 记录如何插入:
INSERT INTO child(code, name, mother_code, father_code) VALUES('001','Jesus', '001', '002');
INSERT INTO child(code, name, mother_code, father_code) VALUES('002','Cain', '003', '004');
INSERT INTO child(code, name, mother_code, father_code) VALUES('003','Abel', '003', '004');
INSERT INTO child(code, name, mother_code, father_code) VALUES('004','Set', '003', '004');
INSERT INTO child(code, name, mother_code, father_code) VALUES('005','Samuel', '005', '006');
And the select
query works how is expected: select
查询的工作方式如何:
mysql> select * from child;
+------+--------+-------------+-------------+
| code | name | mother_code | father_code |
+------+--------+-------------+-------------+
| 001 | Jesus | 001 | 002 |
| 002 | Cain | 003 | 004 |
| 003 | Abel | 003 | 004 |
| 004 | Set | 003 | 004 |
| 005 | Samuel | 005 | 006 |
+------+--------+-------------+-------------+
5 rows in set (0.00 sec)
The goal is get the following: 目标是获得以下信息:
+------+--------+------+-------+-------------+-------------+
| code | name | code | name | mother_code | father_code |
+------+--------+------+-------+-------------+-------------+
| 001 | Mary | 001 | Jesus | 001 | 002 |
| 002 | Joseph | 001 | Jesus | 001 | 002 |
+------+--------+------+-------+-------------+-------------+
I have tried the following: 我尝试了以下方法:
SELECT p.*, c.* FROM parent p,
child c,
(SELECT pm.code AS m_code FROM parent pm) AS m,
(SELECT pf.code AS f_code FROM parent pf) AS f
WHERE
m.m_code='001' AND
f.f_code='002' AND
c.mother_code=m.m_code AND
c.father_code=f.f_code AND
c.mother_code='001' AND
c.father_code='002' AND
c.code='001';
The where
clause would look redundant and it is because I am trying to get the desired result, thus it contains attempts to write correct the query. where
子句看起来很多余,这是因为我试图获得所需的结果,因此它包含尝试编写正确的查询的尝试。
But always returns: 但总是返回:
+------+--------+------+-------+-------------+-------------+
| code | name | code | name | mother_code | father_code |
+------+--------+------+-------+-------------+-------------+
| 001 | Mary | 001 | Jesus | 001 | 002 |
| 002 | Joseph | 001 | Jesus | 001 | 002 |
| 003 | Adan | 001 | Jesus | 001 | 002 |
| 004 | Eva | 001 | Jesus | 001 | 002 |
| 005 | Ana | 001 | Jesus | 001 | 002 |
| 006 | Elcana | 001 | Jesus | 001 | 002 |
+------+--------+------+-------+-------------+-------------+
6 rows in set (0.00 sec)
Thus what is the correct sentence? 那么正确的句子是什么?
Are you just looking for two join
s? 您是否正在寻找两个join
?
select c.*, pm.name as mother_name, pf.name as father_name
from child c join
parent pm
on c.mother_code = pm.code join
parent pf
on c.father_code = pf.code;
You can add a where
clause to filter this down to particular children: 您可以添加where
子句以将其过滤到特定子项:
where c.code in ('001', '002')
From your expected result I think this is what you need: 从您的预期结果中,我认为这是您需要的:
select
p.code, p.name,
c.code, c.name,
c.mother_code, c.father_code
from parent p
inner join child c
on c.mother_code = p.code or c.father_code = p.code
You can add any condition you need with a WHERE clause. 您可以使用WHERE子句添加所需的任何条件。
See the demo . 参见演示 。
Results: 结果:
| code | name | code | name | mother_code | father_code |
| ---- | ------ | ---- | ------ | ----------- | ----------- |
| 001 | Mary | 001 | Jesus | 001 | 002 |
| 002 | Joseph | 001 | Jesus | 001 | 002 |
| 003 | Adan | 002 | Cain | 003 | 004 |
| 004 | Eva | 002 | Cain | 003 | 004 |
| 003 | Adan | 003 | Abel | 003 | 004 |
| 004 | Eva | 003 | Abel | 003 | 004 |
| 003 | Adan | 004 | Set | 003 | 004 |
| 004 | Eva | 004 | Set | 003 | 004 |
| 005 | Ana | 005 | Samuel | 005 | 006 |
| 006 | Elcana | 005 | Samuel | 005 | 006 |
If the dependency is on the child to get the parents, use or on your join. 如果依赖孩子来获得父母,请使用或加入。
SELECT p.Code, p.[Name], c.Code, p.[Name], c.Mother_Code, c.Father_Code
FROM Parent p JOIN Child c ON c.Mother_Code = p.Code OR c.Father_Code = p.Code
WHERE c.name = 'Jesus'
If the dependency is to find a parent's children, then just alter the WHERE statement 如果依赖关系是查找父母的孩子,则只需更改WHERE语句
SELECT p.Code, p.[Name], c.Code, p.[Name], c.Mother_Code, c.Father_Code
FROM Parent p JOIN Child c ON c.Mother_Code = p.Code OR c.Father_Code = p.Code
WHERE p.name IN ('Mary', 'Joseph')
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