如何在 MySQL 中创建带有自引用字段的 table？

Question

在 GTFS 中，字段 parent_station 来自 stop_id（自引用）或 NULL。例如（注意 parent_station 可能是 NULL），

SELECT stop_id, stop_name, parent_station FROM stops where stop_id='1970324837184617' OR parent_station='1970324837184617';

+------------------+----------------------+------------------+
| stop_id          | stop_name            | parent_station   |
+------------------+----------------------+------------------+
| 1970324837184617 | Saint Agne-SNCF      |                  |
| 3377699720880648 | Saint Agne-SNCF      | 1970324837184617 |
| 3377699720880649 | Saint Agne-SNCF      | 1970324837184617 |
| 3377699722011100 | Saint Agne-SNCF      | 1970324837184617 |
| 3377699722011101 | Saint Agne-SNCF      | 1970324837184617 |
| 3377699722914835 | Saint Agne Gare SNCF | 1970324837184617 |
+------------------+----------------------+------------------+
6 rows in set (0,01 sec)

我创建了一个自引用 table：

CREATE TABLE `stops` (
    stop_id VARCHAR(255) NOT NULL PRIMARY KEY,
    stop_code VARCHAR(255),
    stop_name VARCHAR(255),
    stop_desc VARCHAR(255),
    stop_lat DECIMAL(8,6),
    stop_lon DECIMAL(8,6),
    location_type INT(2),
    parent_station VARCHAR(255),
    -- the field `parent_station` might be blank (NULL)
    FOREIGN KEY parent_station REFERENCES stops(stop_id)  -- self-referential table fields
);

但是遇到问题，

ERROR 1064 (42000) at line 99: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'FOREIGN KEY parent_station REFERENCES stops(stop_id)
)' at line 11

在@Awita 的帮助下，我更正了语法并成功创建了 table。

FOREIGN KEY (parent_station) REFERENCES stops(stop_id)

但是加载本地数据时出现了一个新问题。

LOAD DATA LOCAL INFILE 'stops.txt' INTO TABLE stops FIELDS TERMINATED BY ',' IGNORE 1 LINES;

错误：

ERROR 1452 (23000) at line 140: Cannot add or update a child row: a foreign key constraint fails (`paris_gtfs`.`stops`, CONSTRAINT `stops_ibfk_1` FOREIGN KEY (`parent_station`) REFERENCES `stops` (`stop_id`))

此问题是由 NULL parent_station?

引起的

Answer 1

我尝试在使用此命令创建 table 后添加外键并且它有效：

ALTER TABLE stops
ADD FOREIGN KEY (parent_station)
REFERENCES stops(stop_id)

Answer 2

这是一个简单的语法错误。试试这个：

FOREIGN KEY (parent_station) REFERENCES stops(stop_id)

如何在 MySQL 中创建带有自引用字段的 table？

How do I create a table with self-referencing fields in MySQL?

mysql

foreign-keys

create-table

self-reference

gtfs