小结

最近在使用MySQL8.0.37过程中返回的两个错误（Error Code: 3780和Communications link failure），进行了解决。

问题及解决

Error Code: 3780. Referencing column ‘xxx’ and referenced column ‘xxx’ in foreign key constraint ‘zzz’ are incompatible

出更 这个问题的原因是因为数据表的COLLATE属性不匹配，对数据表的创建进行以下修改：

/* Create Tables */

CREATE TABLE `XXX_LIST`
(
	`XXXID` VARCHAR(20) NOT NULL,
	`CONFIGURATIONID` INT NOT NULL,
	CONSTRAINT `PK_XXX_LIST_CONFIGURATION` PRIMARY KEY (`XXXID` ASC)
) 
；

修改COLLATE属性一致，问题解决。

/* Create Tables */

CREATE TABLE `XXX_LIST`
(
	`XXXID` VARCHAR(20) NOT NULL,
	`CONFIGURATIONID` INT NOT NULL,
	CONSTRAINT `PK_XXX_LIST_CONFIGURATION` PRIMARY KEY (`XXXID` ASC)
) ENGINE=InnoDB 
    DEFAULT CHARSET=latin1 
    COLLATE latin1_swedish_ci;
；

com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure

具体报错如下：

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
	at com.mysql.cj.jdbc.exceptions.SQLError.createCommunicationsException(SQLError.java:174) ~[mysql-connector-j-8.3.0.jar:8.3.0]
	at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:64) ~[mysql-connector-j-8.3.0.jar:8.3.0]
	at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:815) ~[mysql-connector-j-8.3.0.jar:8.3.0]
	at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:438) ~[mysql-connector-j-8.3.0.jar:8.3.0]
	at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:241) ~[mysql-connector-j-8.3.0.jar:8.3.0]
	at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:189) ~[mysql-connector-j-8.3.0.jar:8.3.0]
    。。。。。。 省略   。。。。。。
Caused by: com.mysql.cj.exceptions.CJCommunicationsException: Communications link failure

进行各种检查，发现数据库连接有问题，进行相应的重置，问题解决。

参考

stackoverflow: Error when foreign referencing in mySQL (Error 3780)
stackoverflow: com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure Spring boot