MYSQL

Question

架构查询

-- GRAPH INFO TABLE--------------------------------------------------------------

CREATE TABLE GRAPH
(
    graph_id         CHAR(32)       NOT NULL   PRIMARY KEY,
    name             VARCHAR(1024)  NOT NULL
);

INSERT INTO GRAPH set graph_id = MD5('graph1'),
                      name = 'graph1';
                               
INSERT INTO GRAPH set graph_id = MD5('graph2'),
                      name = 'graph2';
                      
INSERT INTO GRAPH set graph_id = MD5('graph3'),
                      name = 'graph3';
                      
-- FIELD INFO TABLE--------------------------------------------------------------

CREATE TABLE FIELD_TEST
(
    field_id    CHAR(50)        NOT NULL   PRIMARY KEY,
    name        VARCHAR(500)    NOT NULL
);

INSERT INTO FIELD_TEST set field_id = MD5('field1'),
                           name = 'field1';
                               
INSERT INTO FIELD_TEST set field_id = MD5('field2'),
                           name = 'field2';
                      
INSERT INTO FIELD_TEST set field_id = MD5('field3'),
                           name = 'field3';
                           
-- GRAPH FIELD RELATION TABLE-----------------------------------------------------

CREATE TABLE GRAPH_FIELD_INFO_TEST
(
    field_id    CHAR(32)                                   NOT NULL,
    graph_id    CHAR(32)                                   NOT NULL,
    PRIMARY KEY (graph_id, field_id),
    CONSTRAINT GRAPH_FIELD_INFO_TEST_FIELD_field_id_fk
        FOREIGN KEY (field_id) REFERENCES FIELD_TEST (field_id)
            ON UPDATE CASCADE ON DELETE CASCADE,
    CONSTRAINT GRAPH_FIELD_INFO_TEST_GRAPH_STORAGE_graph_id_fk
        FOREIGN KEY (graph_id) REFERENCES GRAPH (graph_id)
            ON UPDATE CASCADE ON DELETE CASCADE
);

INSERT INTO GRAPH_FIELD_INFO_TEST set field_id = MD5('field1'),
                                      graph_id = MD5('graph1');
                                      
INSERT INTO GRAPH_FIELD_INFO_TEST set field_id = MD5('field2'),
                                      graph_id = MD5('graph2');     
                                      
INSERT INTO GRAPH_FIELD_INFO_TEST set field_id = MD5('field3'),
                                      graph_id = MD5('graph3');

更新查询

UPDATE FIELD_TEST
SET name     = 'new field1',
    field_id = MD5('new field1')
WHERE field_id = MD5('field1');

错误

Query Error: Error: ER_ROW_IS_REFERENCED_2: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`GRAPH_FIELD_INFO_TEST`, CONSTRAINT `GRAPH_FIELD_INFO_TEST_FIELD_field_id_fk` FOREIGN KEY (`field_id`) REFERENCES `FIELD_TEST` (`field_id`) ON DELETE CASCADE ON UPDATE CASCADE)

如果我更改 FIELD_TEST 的 ID，

修改GRAPH_FIELD_INFO_TEST ID 参考FIELD_TEST,

的ID

我在GRAPH_FIELD_INFO_TEST中设置为级联。

但是，由于以下错误，它失败了。

如果我更改GRAPH的ID，它可以正常工作，

但只有更改FIELD_TEST的ID才能正常工作

请问错误原因？

Answer 1

你的 FIELD_TEST table 中的 field_id 是 CHAR(50)，但你的 GRAPH_FIELD_INFO_TEST table 中的 CHAR(32) ].

CHAR是一个定长类型，所以当你在FIELD_TESTtable系统中更新field_id还尝试使用 CHAR(50) 更新引用列，这当然会失败（尽管实际值只有 32 个字符）。因此错误。将 field_id 列更改为在所有 table 中具有相同的长度...如您的 db-fiddle 中所述，它适用于 GRAPH... 关系，因为所有字段table长度相同。

是的，它在您插入数据时起作用，因为 'foobar' = 'foobar' 即使其中一个来自 CHAR(50) 列而另一个来自 CHAR(32) 列。所以当你在你的 child table 中插入时，它可以在 parent table 中找到相应的键。但是当 parent 键长于 child.

时，它不能进行级联更新

MYSQL - 无法更新父行：外键约束失败

MYSQL - Cannot update a parent row: a foreign key constraint fails

sql

foreign-keys