mysql:通过JDBC接口执行创建触发器的SQL语句

delimiter

以下是从mysql官方文档《23.3.1 Trigger Syntax and Examples》抄来的一段创建触发器的SQL脚本，

delimiter //
CREATE TRIGGER upd_check BEFORE UPDATE ON account
FOR EACH ROW
BEGINIF NEW.amount < 0 THENSET NEW.amount = 0;ELSEIF NEW.amount > 100 THENSET NEW.amount = 100;END IF;
END;//
delimiter ;

这个脚本在MySQL 终端(MySQL console)或Workbench工作正常。但当我通过JDBC接口执行这段SQL代码时报错了

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: 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 'delimiter //

原因是因为delimiter关键字不是SQL标准的一部分,只在Mysql Console有效

所以只要删除delimiter相关的语句就可以了

CREATE TRIGGER upd_check BEFORE UPDATE ON account
FOR EACH ROW
BEGINIF NEW.amount < 0 THENSET NEW.amount = 0;ELSEIF NEW.amount > 100 THENSET NEW.amount = 100;END IF;
END;

allowMultiQueries

有的时候需要反复执行触发器创建命令，为了确保创建触发器成功，在执行CRETAE TRIGGER语句之前，要先执行DROP TRIGGER命令删除已有的同名触发器，如下：

DROP TRIGGER IF EXISTS upd_check ;
CREATE TRIGGER upd_check BEFORE UPDATE ON account
FOR EACH ROW
BEGINIF NEW.amount < 0 THENSET NEW.amount = 0;ELSEIF NEW.amount > 100 THENSET NEW.amount = 100;END IF;
END;

通过JCBC接口执行又会报错：

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: 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 'CREATE TRIGGER upd_check BEFORE UPDATE ON account

这是因为MySQL 的 JDBC 连接器有一个名为allowMultiQueries 的安全特性，默认为false[关闭]. 关闭时，不允许一次执行多个SQL语句。

所以要在数据库的连接url中添加&allowMultiQueries=true就可以解决此问题。
如果不希望修改数据连接URL,而且直接JDBC连接数据库，可以调用Connection java.sql.DriverManager.getConnection(String url, Properties info) throws SQLException方法，将allowMultiQueries通过Properties对象传递给JDBC连接方法，示例代码如下：

 /*** JDBC接口执行SQL脚本* @param sql SQL代码* @throws SQLException*/public void runSQL(String sql) throws SQLException{Connection connection = null;Statement stat = null;try {String url = "jdbc:mysql://localhost:3306/test?characterEncoding=utf8&useInformationSchema=true";//&allowMultiQueries=true// 加载并注册MySQL的JDBC驱动Class<?> driverClass = Class.forName("com.mysql.jdbc.Driver");DriverManager.registerDriver(Driver.class.cast(driverClass.newInstance()));Properties info=new Properties();// 设置连接用户名info.put("user", "root");// 设置允许执行多条SQL语句info.put("allowMultiQueries","true");connection = DriverManager.getConnection(url, info);System.out.printf("sql string:\n" + sql + "\n");stat = connection.createStatement();stat.executeUpdate(sql);         } catch (Exception e) {e.printStackTrace();}finally{if(null != stat){stat.close();}if(null != connection){connection.close();}}}

参考资料

《23.3.1 Trigger Syntax and Examples》
《Error while creating trigger through JDBC on mysql5.5》
《6.3.5 Security》
《allowMultiQueries flag with JDBC and jOOQ》