MySQL版本是8.0.3，数据库连接字符串都检查无误，驱动类名加不加cj都试过了，URL是否加时区、是否加useSSL都试过了，都无法正常登录进去！

我在运行library这个web程序登录时（我的MySQL版本是8.0.3，数据库连接字符串都检查无误，驱动类名加不加cj都试过了，URL是否加时区、是否加useSSL都试过了，都无法正常登录进去！），提示错误分如下两种情况：

1、当我使用您工程默认的mysql-connector-java(5.1.6)时，用admin/123456登录提示错误：

### Error querying database.  Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection; nested exception is java.sql.SQLException: Connections could not be acquired from the underlying database!

### The error may exist in com/yanzhen/dao/AdminMapper.xml

### The error may involve com.yanzhen.dao.AdminMapper.queryUserByNameAndPassword

### The error occurred while executing a query

### Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection; nested exception is java.sql.SQLException: Connections could not be acquired from the underlying database!

2、当我使用mysql-connector-java(8.0.9-rc)时，用admin/123456登录提示错误：

### Error querying database.  Cause: java.sql.SQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'admin where username = 'admin'

and password = '123456'' at line 1

### The error may exist in com/yanzhen/dao/AdminMapper.xml

### The error may involve com.yanzhen.dao.AdminMapper.queryUserByNameAndPassword-Inline

### The error occurred while setting parameters

### SQL: select * from admin where username = ? and password = ?

### Cause: java.sql.SQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'admin where username = 'admin' and password = '123456'' at line 1

问题分析：

数据中的表名为admin，而admin在MySQL8.0.3中已经变成关键字了，二者冲突了。Mysql5.7没限制。其它被Mysql8占用的关键字还有：member,order,admin,leave。如果表名写成member,order,admin,leave等就会报错，暂时发现这几个...好坑呀...

解决办法：

方法（1），改掉表名，不使用关键字。

方法（2），给表名加上反单引号``符号（是tab键上方那个键）。