MySQL：添加外键约束失败

如何解决MySQL：添加外键约束失败

我有两个表clinics和consultations。
每个咨询记录都属于一个诊所，因此我想将clinic_name设置为引用clinic_name表中clinics的外键。但这会引发错误：

code: 'ER_FK_NO_INDEX_PARENT',errno: 1822,sqlMessage: "Failed to add the foreign key constraint. Missing index for constraint 'consultations_ibfk_1' in the referenced table 'clinics'",

诊所表：

const sql_createclinics =
  "CREATE TABLE IF NOT EXISTS clinics(" +
  "id INT AUTO_INCREMENT," +
  "email VARCHAR(255) NOT NULL," +
  "password VARCHAR(255) NOT NULL," +
  "clinic_name VARCHAR(255) NOT NULL," +
  "phone_num VARCHAR(15) NOT NULL," +
  "address VARCHAR(255) NOT NULL," +
  "PRIMARY KEY (id))";

**咨询表：**

const sql_createconsult =
  "CREATE TABLE IF NOT EXISTS consultations(" +
  "id INT AUTO_INCREMENT," +
  "clinic_name VARCHAR(255)," +
  "doctor_name VARCHAR(255)," +
  "patient_name VARCHAR(255)," +
  "diagnosis VARCHAR(255)," +
  "medication VARCHAR(255)," +
  "consultation_fee FLOAT," +
  "datetime DATETIME DEFAULT CURRENT_TIMESTAMP," +
  "PRIMARY KEY (id)," +
  "FOREIGN KEY (clinic_name) REFERENCES clinics(clinic_name))";

解决方法

外键应引用另一个表中的单个记录。 使用您的架构定义，您不能保证clinic_name是唯一的。如果clinics.clinic_name是唯一的，则通过为其创建唯一索引来在数据库中强制它。否则，请勿使用climate_name作为外键，而应将诊所的id纳入考虑范围，并使用id创建外键约束。

与临床ID有关：

const sql_createconsult =
"CREATE TABLE IF NOT EXISTS consultations(" +
"id INT AUTO_INCREMENT," +
"clinic_id INT," +
"doctor_name VARCHAR(255)," +
"patient_name VARCHAR(255)," +
"diagnosis VARCHAR(255)," +
"medication VARCHAR(255)," +
"consultation_fee FLOAT," +
"datetime DATETIME DEFAULT CURRENT_TIMESTAMP," +
"PRIMARY KEY (id)," +
"FOREIGN KEY (clinic_id) REFERENCES clinics(clinic_id))";

,

您可以尝试以下方法：

CREATE TABLE IF NOT EXISTS consultations( 
  id INT,clinic_name VARCHAR(255),doctor_name VARCHAR(255),patient_name VARCHAR(255),diagnosis VARCHAR(255),medication VARCHAR(255),consultation_fee FLOAT,datetime DATETIME DEFAULT CURRENT_TIMESTAMP,FOREIGN KEY (id) REFERENCES clinics(id));