MySQL 错误号 : 150 "Foreign key constraint is incorrectly formed"

Question

有谁知道为什么我会收到以下错误消息？

errno: 150 "Foreign key constraint is incorrectly formed"

CREATE TABLE meter (
    `code` CHAR(5) NOT NULL,
    `type` VARCHAR(30) NOT NULL,
    description VARCHAR(30) NULL,
    location_code CHAR(3) NOT NULL,
CONSTRAINT pri_meter 
    PRIMARY KEY (`code`),
CONSTRAINT for_meter
    FOREIGN KEY (location_code) REFERENCES location (`code`));

CREATE TABLE location(
    `code` CHAR(3) NOT NULL,
    company VARCHAR(30),
    `type` VARCHAR(30),
CONSTRAINT pri_location 
    PRIMARY KEY (`code`));

CREATE TABLE reading(
    meter_code CHAR(5) NOT NULL,
    `when` DATETIME NOT NULL,
    display DECIMAL(9,3) NOT NULL,
    estimate BIT NOT NULL,
CONSTRAINT pri_reading 
    PRIMARY KEY (`when`, meter_code),
CONSTRAINT for_reading
    FOREIGN KEY (meter_code) REFERENCES meter (`code`));

CREATE INDEX index_meter ON meter (location_code);
CREATE INDEX index_reading ON reading (meter_code);

Answer 1

首先创建location 表。

当被引用的表还不存在时，您不能引用表列。

在您的示例中，您在创建 meter 表时引用了表 location。