使用SQL将表中的两行合并为一行

我正在尝试编写一个SQL查询（在Oracle DB中），它执行以下操作：

表:

Id | Name  | Father_id

1  | John  | 2
2  | Peter |
3  | Ann   | 2

预期结果：

Name  | Father_Name

John    Peter
Ann     Peter

我想把所有有父亲的人和父亲的名字列在一起。用户可以（当然）有最多一个父亲，但不一定有一个

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写这样一个查询的最佳方式是什么？

自联接，如果你想要没有父亲的孩子，就做一个左外联接

select *
from table t_child join 
     table t_father on t_child.father_id = t_father.id

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试试这个sql，它肯定会工作的

select child.MenuName as ChildName,parent.MenuName as ParentName from table_name as child
left join table_name as parent on child.parentId = parent.MenuId

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您需要使用left，因为您提到不一定需要使用一个自联接（和两个表/索引扫描），而是可以使用分层查询：

Oracle 11g R2架构设置：

CREATE TABLE people ( Id, Name, Father_id ) AS
SELECT 1, 'John',  2    FROM DUAL UNION ALL
SELECT 2, 'Peter', NULL FROM DUAL UNION ALL
SELECT 3, 'Ann',   2    FROM DUAL

SELECT name,
       PRIOR name AS father_name
FROM   people
WHERE  LEVEL > 1
OR     CONNECT_BY_ISLEAF = 0     -- Comment out if you do not want Peter,NULL
CONNECT BY PRIOR id = father_id

|  NAME | FATHER_NAME |
|-------|-------------|
| Peter |      (null) |
|  John |       Peter |
|   Ann |       Peter |

查询1：

CREATE TABLE people ( Id, Name, Father_id ) AS
SELECT 1, 'John',  2    FROM DUAL UNION ALL
SELECT 2, 'Peter', NULL FROM DUAL UNION ALL
SELECT 3, 'Ann',   2    FROM DUAL

SELECT name,
       PRIOR name AS father_name
FROM   people
WHERE  LEVEL > 1
OR     CONNECT_BY_ISLEAF = 0     -- Comment out if you do not want Peter,NULL
CONNECT BY PRIOR id = father_id

|  NAME | FATHER_NAME |
|-------|-------------|
| Peter |      (null) |
|  John |       Peter |
|   Ann |       Peter |

：

CREATE TABLE people ( Id, Name, Father_id ) AS
SELECT 1, 'John',  2    FROM DUAL UNION ALL
SELECT 2, 'Peter', NULL FROM DUAL UNION ALL
SELECT 3, 'Ann',   2    FROM DUAL

SELECT name,
       PRIOR name AS father_name
FROM   people
WHERE  LEVEL > 1
OR     CONNECT_BY_ISLEAF = 0     -- Comment out if you do not want Peter,NULL
CONNECT BY PRIOR id = father_id

|  NAME | FATHER_NAME |
|-------|-------------|
| Peter |      (null) |
|  John |       Peter |
|   Ann |       Peter |

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做一个自联接。在这个时代，我们可以有很多父亲。：）