为什么执行这些表时会出现错误1452？ [重复]

Question

此问题已经在这里有了答案：

• ERROR 1452: Cannot add or update a child row: a foreign key constraint fails11个答案

我想在一些表中插入一些数据。但是，到达statistics_per_year后，mysql会弹出错误代码1452，但我不知道为什么会这样。

错误：

17:54:58    INSERT INTO statistics_per_year(disease_continent_id,infected_id,dead_id) VALUES(2,3,4) Error Code: 1452. Cannot add or update a child row: a foreign key constraint fails (`practice`.`statistics_per_year`, CONSTRAINT `statistics_per_year_ibfk_1` FOREIGN KEY (`infected_id`) REFERENCES `statistics_reference` (`infected_id`))    0.484 sec

代码：

CREATE TABLE df(
    disease_continent_id INT NOT NULL PRIMARY KEY 
);
CREATE TABLE statistics_reference(
    infected_id INT NOT NULL,
    dead_id INT NOT NULL,
    per_100000_population VARCHAR(30) NOT NULL,
    PRIMARY KEY(infected_id)
);
CREATE TABLE statistics_per_year(
    disease_continent_id INT NOT NULL,
    infected_id INT NOT NULL,
    dead_id INT NOT NULL,
    FOREIGN KEY(infected_id) REFERENCES statistics_reference(infected_id),
    FOREIGN KEY(disease_continent_id) REFERENCES df(disease_continent_id)
);
INSERT INTO df(disease_continent_id)
VALUES(1);
INSERT INTO statistics_reference(infected_id,dead_id,per_100000_population)
VALUES(1,2,"fff");
INSERT INTO statistics_per_year(disease_continent_id,infected_id,dead_id)
VALUES(1,3,4);

Answer 1

您的模式停留：

CREATE TABLE statistics_per_year(
    ...
    FOREIGN KEY(infected_id) REFERENCES statistics_reference(infected_id),
    ...
);       

这意味着：您在statistics_per_year(infected_id)中插入的每个值都必须在statistics_reference(infected_id)中。

---

您愿意：

INSERT INTO statistics_reference
    (infected_id,dead_id,per_100000_population) 
    VALUES(1,2,"fff");
INSERT INTO statistics_per_year
    (disease_continent_id,infected_id,dead_id) 
    VALUES(1,3,4);

表statistics_reference仅包含一个记录，并带有infected_id = 1。您正在尝试使用statistics_per_year在相关表infected_id = 3中插入一条记录。失败是因为statistics_reference中没有该值的父记录。

您可以在statistics_reference中插入丢失的父记录，或在子表中更改insert以引用现有的父ID。