MySQL:检查用户是否存在并删除它

Question

没有标准的方法来检查MySQL用户是否存在并且基于该用户丢弃它.这有什么变通方法吗？

编辑:我需要一个直接的方式来运行它而不会抛出错误,
例如

DROP USER test@localhost; :    

Answer 1

这对我有用:

GRANT USAGE ON *.* TO 'username'@'localhost';
DROP USER 'username'@'localhost';

如果用户尚不存在(并授予其无害特权),则会创建用户,然后以任一方式删除它.找到解决方案:http://bugs.mysql.com/bug.php？id = 19166

更新:@Hao建议添加IDENTIFIED BY; @andreb(在评论中)建议禁用NO_AUTO_CREATE_USER.

Answer 2

从MySQL 5.7开始你可以做到 DROP USER IF EXISTS test

更多信息:http://dev.mysql.com/doc/refman/5.7/en/drop-user.html

Answer 3

从一个MySQL论坛找到了答案.我们需要使用一个过程来删除用户.

这里的用户是"test"和"databaseName"数据库名称.

SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='ANSI';
USE databaseName ;
DROP PROCEDURE IF EXISTS databaseName.drop_user_if_exists ;
DELIMITER $$
CREATE PROCEDURE databaseName.drop_user_if_exists()
BEGIN
  DECLARE foo BIGINT DEFAULT 0 ;
  SELECT COUNT(*)
  INTO foo
    FROM mysql.user
      WHERE User = 'test' and  Host = 'localhost';
   IF foo > 0 THEN
         DROP USER 'test'@'localhost' ;
  END IF;
END ;$$
DELIMITER ;
CALL databaseName.drop_user_if_exists() ;
DROP PROCEDURE IF EXISTS databaseName.drop_users_if_exists ;
SET SQL_MODE=@OLD_SQL_MODE ;


CREATE USER 'test'@'localhost' IDENTIFIED BY 'a';
GRANT ALL PRIVILEGES  ON databaseName.* TO 'test'@'localhost'
 WITH GRANT OPTION

Answer 4

对于phyzome的答案(最受高度评价的答案),在我看来,如果你在grant语句的末尾加上"identify by",那么将自动创建用户.但是如果不这样做,则不会创建用户.以下代码适用于我,

GRANT USAGE ON *.* TO 'username'@'localhost' IDENTIFIED BY 'password';
DROP USER 'username'@'localhost';

希望这可以帮助.

Answer 5

更新

从 MySQL 5.7 开始，您可以直接使用DROP USER IF EXISTS语句。 https://dev.mysql.com/doc/refman/5.7/en/drop-user.html

DROP USER IF EXISTS 'user'@'localhost';

仅供参考（对于旧版本的 MySQL），这是一个更好的解决方案......！！！

以下 SP 将帮助您'tempuser'@'%'通过执行来删除用户CALL DropUserIfExistsAdvanced('tempuser', '%');

如果你想删除所有名为'tempuser'（例如'tempuser'@'%'、'tempuser'@'localhost'和'tempuser'@'192.168.1.101'）的用户，请执行 SP ，CALL DropUserIfExistsAdvanced('tempuser', NULL);这将删除所有名为tempuser!!!的用户 严重地...

现在请看一下提到的 SP DropUserIfExistsAdvanced：

DELIMITER $$

DROP PROCEDURE IF EXISTS `DropUserIfExistsAdvanced`$$

CREATE DEFINER=`root`@`localhost` PROCEDURE `DropUserIfExistsAdvanced`(
    MyUserName VARCHAR(100)
    , MyHostName VARCHAR(100)
)
BEGIN
DECLARE pDone INT DEFAULT 0;
DECLARE mUser VARCHAR(100);
DECLARE mHost VARCHAR(100);
DECLARE recUserCursor CURSOR FOR
    SELECT `User`, `Host` FROM `mysql`.`user` WHERE `User` = MyUserName;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET pDone = 1;

IF (MyHostName IS NOT NULL) THEN
    -- 'username'@'hostname' exists
    IF (EXISTS(SELECT NULL FROM `mysql`.`user` WHERE `User` = MyUserName AND `Host` = MyHostName)) THEN
        SET @SQL = (SELECT mResult FROM (SELECT GROUP_CONCAT("DROP USER ", "'", MyUserName, "'@'", MyHostName, "'") AS mResult) AS Q LIMIT 1);
        PREPARE STMT FROM @SQL;
        EXECUTE STMT;
        DEALLOCATE PREPARE STMT;
    END IF;
ELSE
    -- check whether MyUserName exists (MyUserName@'%' , MyUserName@'localhost' etc)
    OPEN recUserCursor;
    REPEAT
        FETCH recUserCursor INTO mUser, mHost;
        IF NOT pDone THEN
            SET @SQL = (SELECT mResult FROM (SELECT GROUP_CONCAT("DROP USER ", "'", mUser, "'@'", mHost, "'") AS mResult) AS Q LIMIT 1);
            PREPARE STMT FROM @SQL;
            EXECUTE STMT;
            DEALLOCATE PREPARE STMT;
        END IF;
    UNTIL pDone END REPEAT;
END IF;
FLUSH PRIVILEGES;
END$$

DELIMITER ;

用法：

CALL DropUserIfExistsAdvanced('tempuser', '%');删除用户'tempuser'@'%'

CALL DropUserIfExistsAdvanced('tempuser', '192.168.1.101');删除用户'tempuser'@'192.168.1.101'

CALL DropUserIfExistsAdvanced('tempuser', NULL);删除所有指定的用户'tempuser'（例如'tempuser'@'%'、'tempuser'@'localhost'和'tempuser'@'192.168.1.101'）